Children's obesity is a known health problem in the world and is a strong predictor of obesity in adulthood which increases the incidence of related diseases such as metabolic syndrome. According to the MONIKA project by the World Health Organization (WHO), Iran is one of the seven countries with a high rate of child obesity. Fatty liver is an abnormality related to metabolic syndrome, with higher prevalence in obese children according to some previous studies. This study investigates the presence of Sonographic Fatty Liver (SFL) in Iranian obese children in comparison with normal and overweight children. This was a cross-sectional study on 962 randomly selected children between the ages of 6 to 18 years. The subjects were divided into three groups of normal, overweight and obese based on body mass index (BMI). A questionnaire including demographic and anthropometric characteristics was filled for each one. To detect the presence of SFL all the subjects underwent assessments with ultrasonography by radiologist who was not aware of their BMI. The incidence of SFL was determined based on the ultrasonographic diagnosis criteria. The average age of the children in the study was 12.59 +/- 3.25 years. The mean of the liver span in the normal, overweight and obese groups were 111.36 +/- 18.73, 121.18 +/- 16.63 and 118.21 +/- 19.15 respectively. The prevalence of SFL in obese children was 54.4%, which was significantly higher than overweight (10.5%) and normal ones (1%). According to present results, there was no significant difference in prevalence of SFL between sexes. The high rate of detected SFL in obese children in this study suggests that Iranian obese children are at risk of metabolic syndrome. Moreover, the WHO indicated Iran as one of the countries with high rate of obese children. Based on this information, we can conclude that the prevalence of metabolic syndrome and its related non-communicable diseases will be increasing future in . Therefore, it is necessary to develop some plan to control overweight problem including teaching healthy lifestyle in schools and kindergartens as well as mass media.