Objectives This study attempted to deeply understand the experiences and nature of loneliness formed by mid-dle-aged unmarried men living alone from childhood to middle age. Methods To this end, five unmarried men in their 40s and 50s were interviewed individually twice from January 2023 to June 2023 to collect data, and Giorgi's phenomenological research method was used to focus on the phe-nomena experienced by research participants. Results As a result of the study, six components and 18 sub-components were derived from ‘loneliness sprouted by childhood wounds’,‘ wandering and accumulating loneliness in puberty’, ‘struggle for sief-reliance and lone-liness’, ‘excitement and conflict and loneliness of finding a spouse’, ‘frustration and increasing loneliness in mar-riage’, ‘acceptance and overcoming loneliness and pain’. Conclusions This study is meaningful in that the essence of the loneliness experience of middle-aged single men living alone is that they have an insight into their own isolated life with distrust, avoidance, and dependence on others due to their parents' inappropriate parenting attitudes and parenting environment in childhood. As a result, it will serve as basic data for expanding a broad understanding of the complex phenomenon of loneliness by illumi-nating individual experiences and social contexts, and preparing single-person household policies for mid-dle-aged single men and measures to live alone in old age.