Obesity is one of the leading public health issues in the world whose significance lies, not only in its prevalence, but also in its consequences i.e. diseases that gradually develop in obese people. The aim of the study was to determine obesity prevalence among school children and the influence of health education on its prevalence. Study included pupils of 19 first grades in 8 primary schools of Osijek-Baranja County, Croatia. Body weight and height, waist and hip circumference were measured. Parameters for assessing obesity: body mass index (BMI, according to Croatian referral values), waist circumference (WC), waist and hip circumference ratio (WHR) and waist circumference and height ratio (WHtR) were measured. In order to determine whether the health education of pupils and their parents influences children's anthropometric indexes, health education regarding correct diet, obesity and its consequences and the need for life style changes in terms of daily physical activity was conducted in four primary schools. Pupils of other four primary schools were measured as a control group. Prevalence of overweight children according to BMI before education was 8.9% (6.5% of overweight and 2.4% of obese children). In intervention group of children, according to BMI, there was no decrease in proportion of obese after the health education was conducted and prevalence was 2% before and after the education. On the second measurement, pupils in control group showed increase in proportion of obese from 2.9% to 3.5%. According to weight circumference and height ratio before education there were 10.2% of obese children. After six months, there was an increase in proportion of obese to 11.3%. According to this index there was an increase in proportion of obese in all groups of pupils regardless of gender and conducted education. This study shows that in school-based obesity programs it is necessary to apply more intense interventions with another type of methodology; program should be conducted continuously during longer period, otherwise this condition will continue to rise.