Adolescence is the stage of human life, which transition from childhood to adulthood. Personality accentuated and where knowledge and habits that can last a lifetime acquired. In what concerns to health education, adolescence is the most difficult period in accepting health education, because it is characterized by non-accepting information advice provided by parents or teachers. There are many risks to health during adolescence, mainly because young people are not care in risks and believe they are not at risk or vulnerable to disease. Personal hygiene is the basic concept of cleaning and it is the first step to good health, it consider as one of the most important part of our daily lives at everywhere (home and workplace) and which help us to avoid disease and protect our health. Appropriate knowledge and practices of personal hygiene plays an important role in prevent communicable diseases. The aim of this study was to assess knowledge of personal hygiene in preparatory student in Riyadh City. About 246 female students were participated in this study through Google forms –create and analyze surveys, selected by convenience sample. Questionnaire included four parts, first part consist of demographic data, health history (personal and menstrual), 2nd part was regarding menstruation hygiene, third part was about personal hygiene, fourth part was about hand hygiene, shower, mouth hygiene. The data collected, tabulated and analyzed by using SPSS V.25, descriptive and inferential statistics employed. There is a definite need for intense personal hygiene education programs in Riyadh City based on preparatory students' needs.