The aim of this study was to examine whether there is a difference in the inclination of altruism among high school students in large and small urban environment. In the first part there is theoretical explanation of prosocial behavior, its development and external and internal factors that affect this behavior. After the theoretical part about prosocial behaviour, the subject of this study – altruism, is explained in a more detailed way. Different theories of altruism development and the psychological, emotional and cognitive processes which affect altruistic behavior have been presented. The theoretical part is followed by the research part, in which the results showed that high school students in the lower urban environment on the altruism scale have statistically more significant results. This is confirmed by the initial assumption that students in the lower environment are more inclined to altruistic behavior, because they know each other better. Also, in the theoretical part, the same opinion is confirmed by explaining how people are more willing to help those with whom they can identify in some way. In addition to the main conclusion of the research, the obtained results have shown that female students tend to be more inclined to altruistic behavior than male students.