In this study, the phenomenon of conversion is analysed in the context of the experiences of Japanese Muslim converts. The purpose of this study is to understand the processes leading to conversion to Islam among Japanese and to explore religious conversion motifs of Japanese Muslim converts, thus making a conceptual contribution to the existing conversion literature. The problems of the research were, understanding the conditions leading Japanese to Islam, exploring circumstances the Japanese had started to develop an interest towards Islam and Muslims, and finally discovering the main motivating factors of their conversion. With this aim, the research has been designed as qualitative research. A combination of phenomenology and grounded theory research methods were applied in order to understand the essence of the conversion experience of Japanese Muslims and also to develop a theoretical explanation for their conversion. A total of 2 years and 3 months, between September 2016 - December 2017 and February 2019 - January 2020, were spent in Tokyo, Japan for the fieldwork. The data is derived from the semi-structured interviews, participant observation and field study notes. Semi-structured interviews were conducted with 32 women and 30 men, in total 62 Japanese Muslims, whose ages are changing between 19 and 81. The participants were reached via snowball and purposive sampling methods. Most of the Japanese Muslims interviewed are from Tokyo, and some reside in other cities in Japan. The events and activities of various mosques, masjids and associations, especially of the Tokyo Mosque and Turkish Cultural Centre and the Japanese Muslim Association, were participated in order to make observations. Additionally, field notes were kept during these visits. Waseda University library and its resources were consulted for the literature research. It is discovered that Japanese conversion to Islam is a social process, led by their encounters with Muslims. Most of the time, their first memorable encounter with Islam took place in the social context, overseas, during their study abroad, business or leisure travel, or at their work and schools, or via their romantic interests within Japan. Few of them got introduced to Islam via media or their personal interests. Upon their encounters, the Japanese, who were not seriously dissatisfied with their existing living conditions and beliefs before, and who were not in search of a new way of life and belief, began to be interested in Islam in different ways. It is also discovered they had a lack of strong prejudice against Islam, thus following their encounters, they had an open attitude learning towards the religion and the people. In this study, four motivational factors discovered influential on Japanese conversion to Islam: social, intellectual, psychological and pragmatic. In social motivations, desires to be included in the Muslim community they encountered, to be like them, and to lead a life them are strong. Participants in this category are interested in human relations, perspectives, attitudes and behaviours of Muslims. They were impressed by the closeness of family relations, by the idea of an international Muslim brotherhood-sisterhood, kindness, sincerity and helpfulness they observed among Muslims, and their courage towards calamities of life. In this group, the participants are most interested in Muslims. In the intellectual motivations, their primary motivation is their conviction of Islam intellectually. The attention of participants was attracted by the theoretical and ideological aspects of Islam, its teachings and its belief system. They began asking questions about Islam to the Muslims around them. Some were convinced by clear, simple and sensible answers they received. Some found similarities between Islam and Japanese culture, and felt close to Islam. Some were interested in the Islamic social system. Lastly, some participants who were Christians previously found Islam as the next logical step they could continue. In the psychological motivations category, the participants are in need of a belief and a quest for a God prior to their encounters. The idea of a God with an infinite power, who can protect them from their fears and anxieties and who can always watch over them attracted them. Most of the participants in this category, while describing their experiences, explained that they realised their need following their encounters with Islam and Muslims. Few had emotional experiences hearing the sound of the adhan and the Qur’an, and participating in the prayer. The last motivations are the pragmatic ones. In this category, Islam and conversion are instruments for participants who had other interests. Some converted for marriage with their Muslim partners, some for business and scholarship opportunities.