Abstract: In order to determine the association between Giardia infection and nutritional status, a cross- sectional study was performed on twenty randomly selected primary schools from two regions of Ardabil province in 2005. Anthropometric factors including height, weight and midarm muscle circumference (MAC) were measured for 813 children (413 males, 400 females). The food intake was estimated for energy and other nutrients by 24 h recall method for three days in week. Determination of Giardia infection was done by using direct wet mount and formalin-ether sedimentation concentration.10.9% of boys and 17.2% of girls were infected with Giardia infection. Weight and MAC in none infected girls and boys (only 7 and 11 years old) were higher than in infected groups. The average values for weight, height and MAC for both genders were lower than those of NCHS values. Vitamin E and phosphorous intake in non infected boys (in 7-10 years old) were less than infected boys. Calorie, protein, vitamins (B3, B5, B6, E and folacin) and minerals (copper, magnesium, phosphorous, potassium and selenium) intake of infected girls were less than non infected girls in 11-12 years old category. Based on the results found in this study, we conclude that Giardia infection may affect on some of anthropometric factors as well as the calorie and other nutrients intake in some of age groups.