Giardia lamblia is the worldwide most common intestinal protozoan parasite. It was indicated that Giardia is the most important agent that causes acute and chronic diarrhea in infants, young children and travelers. The aim was to detect the influence of host HLA alleles on the susceptibility to infection with G. lamblia in a sample of Iraqi patients. A total of (40) patients with giardiasis aged (14-39) years were registered. All of them were symptomatic and (40) healthy individuals matched age and sexes were included as controls. All patients were prepared to stool examination to detect G. lamblia and eliminated other pathogens, as well as human leukocyte antigen (HLA) class II alleles (DRB1) typing. The most common detected alleles in patients group were HLA-DRB1*03:0101, HLA-DRB1*13:0101,and HLA-DRB1*07:0101 compared to control group (P< 0.003; odds ratio (OR) 6.32; 95% confidence interval (CI) 2.35 to 28.03), secondly (P < 0.002; odds ratio (OR) 4.27; 95% confidence interval (CI) 1.64 to 8.05) and lastly (P< 0.001; odds ratio (OR) 3.54; 95% confidence interval (CI) 1.22 to 5.68) respectively. In conclusion HLA- DRB1*03:0101 alleles,*13:0101 alleles and 07:0101 alleles may affect human susceptibility to giardiasis