Background: Malnutrition, both under and over, is a serious public health problem related to increased risk of mortality, morbidity and overall development of children. Coexistence of undernutrition and overnutrition among Indian children has been reported. Objective: To investigate the association between body mass index and IQ of rural primary school children. Methods: A community based cross-sectional and descriptive study was undertaken in Government rural primary schools of Shimulpur, Salka, Kumarhut, Ramnagar in the districts 24 Parganas North and South, West Bengal, India among 560 children aged 6 to 8 years (class II to IV). Anthropometric measurements were taken to assess body mass index. Raven__ampersandsignrsquo;s Progressive Matrices Test was done to determine IQ grades of these students. Results: 28.03% and 28.75% of rural primary school children under study were wasted and severely wasted, respectively while 3.39% and 1.08% were overweight and obese according to BMI. Only 0.37% and 50.71% of rural children had 95th (intelligently superior) and 5th (intelligently impaired) percentile of IQ grades. Body mass index of children has significant positive correlation with IQ (P? 0.05). Conclusions: Higher body mass index is associated with lower IQ grades in rural children.