This study investigated the middle and high school students' interests towards the subjects of human biology. specifically, "Human Health and Nutrition" and "Human Body and Organs." The study also investigated sources of their interests and factors that impact their interests, namely people that they interact and courses that they take about biology and science. 972 students from fifth through tenth grades in 17 schools in Ankara participated in this study. The results show that students' interests towards human biology in general do not change from fifth to tenth grade. However, students' interests towards various subjects of biology were decreased. Ninth grade students reported the lowest interest among the grades investigated towards the subject of "Human Health and Nutrition" and "Human Body and Organs." Factors such as students' interest in sports, their health concerns, and their desire to protect themselves from diseases might have effected the formation of their interests towards these subjects.