The aim of this research was to determine whether there is a statistically significant relationship between the quality of free time of preschool children and their body mass index. The research was conducted on a sample of 108 preschool children between the ages of 4 and 7. In the research, 58 boys and 50 girls attending kindergarten in the city of Zagreb were examined. An anonymous survey questionnaire was used to collect data, which was filled out by the parents of the respondents with information on height, age, body weight and various questions about their children's free time. Based on the collected answers, quality of free time points were assigned, and each respondent scored a certain number of points on the quality of free time scale. Based on data on height and body mass, the body mass index was calculated. The correlation between the variables was tested with the Pearson test and showed a moderate negative correlation between the variables, i.e. a decrease in the body mass index closer to the recommended values of the subjects with an increase in the quality of free time. The obtained results show that free time has a measurable impact on BMI, but it is not the only factor that affects BMI. Namely, some of the factors are the family environment, diet, cultural circumstances, etc. therefore, it is necessary to do further research in order to be able to examine all the factors that influence BMI.