Abstract Giardia lamblia is a pathogenic protozoan parasite of medical and evolutionary importance and its very important causative agent of diarrhea and other symptoms in human. The objectivewas demonstrate the effect of Giardia lambila infection on some biochemical parameters in infected children and who diagnosed with diarrhea in the children hospital and other hospitals in Diyala city, Iraq during the period 1 February to 30 October, 2019. (300) feces samples were examined for infants patients with diarrhea in (0-5) years, the examination of these samples demonstrated positive results with G. lambila 108/200 (36%), the biochemical tests and hematological values of the patients demonstratednon-significant (P<0.05) differences in Hb level, PCV and significant (P<0.05) elevate in WBC count in the infected infants children to the control group, the biochemical study demonstrated decrease in the concentration of iron and ferritin level and catalase (CAT) with significant (P<0.05) increase in Malondialdehyde (MDA) in patients compared to the control group.