The aim of this study was to examine how children perceive their body size and whether their actual or perceived body size can explain their anti-fat views. Four hundred and fourteen 5-6, 7-8 and 9-10-year-old children were read short vignettes depicting two characters, one possessing a positive and the other a negative quality. Following each vignette, participants were asked to pick the story characters among thin, average and obese figures. Obesity bias was defined as the attribution of the positive quality to the thin or average figure and the corresponding negative one to the obese. Body mass index determined children's actual body size. Perceived body size was determined with the use of Collins' (1991) figures of increasing size. The results showed that actual body size affected the accuracy of perceived body size. While the majority of average children were accurate at identifying their body size, most overweight and obese children tended to underestimate it. The accuracy of body size perception improved with age. Obesity bias did not relate to children's actual but to their perceived body size: Those who perceived themselves as heavier exhibited less bias. The implications of the findings are discussed in relation to children's developing identity, and suggestions are made for future research.