In today's society, there is an increasing phenomenon of obesity in people of all ages, but particularly the worrying occurrence of obesity in childhood. That is why the obesity of children is a serious public health problem. The purpose of writing this graduate thesis was to determine the condition of students’ obesity regarding the involvement in extracurricular sports activities and out of school activity. A sample of 64 students (both sexes) of the fourth grade of primary school in Zagreb was collected for the research needs. To assess the indicators of the obesity condition, respondents were measured in the following: body height, body mass, subcutaneous fatty tissue - skin folds on the back and skin folds on the upper arm, hip and waist circumference. Statistical data processing presented basic descriptive parameters and a T-test was used to determine statistically significant differences in the indicators of the obesity status of the students involved and those not involved in sports activities. Furthermore, in order to assess the correlation between the indicators of the condition of obesity and the quality of spending free time, a questionnaire was conducted. A correlation analysis of the indicators of obesity and the results of the questionnaire survey was made to establish a statistically significant correlation. The results show that there is no statistically significant difference in the indicators of the condition of the students involved and those not involved in sports activity. It was also found that there was no statistically significant association between the indicators of the condition of obesity and the quality of leisure time. It was also evident that students are more involved in the out of school activities than in extracurricular activities. Namely, the results of the research suggest that students involved in sports activities have a lower body mass index compared to students not involved in sports activities with lower body activity in their free time, and higher television viewing activity, but it is not statistically significant. Also, considering the percentage of body fat, it has been found that most of the students involved in sports activities are normally fed, while among the students who are not involved in sports activities there is a significant number of those with excessive body weight. Students should certainly be encouraged to engage in sports activities because the presence of excessive body weight can continue in adulthood and result in obesity.