Objective: The current research aimed to evaluate the concentration level of IL-5 in irritable bowel syndrome patients infected with Blastocystis infection Methods: Stool samples were collected from 156 of respondents(78 patients were diagnosed clinically by physician suffering from IBS and 78 control apparently healthy individuals without any history of disease) attended to three Hospitals in Al-Najaf Province of Iraq from August, to December 2019. Data was collected using self-administrated questionnaire. The whole questionnaire has five sections which included age, sex , family income, living area and occupation.Fecal specimens were collected and each sample divided into three parts, the first for microscopic examination and second for culture and thrid part were quickly frozen for Immunological evaluation of IL-3 by Sandwich ELISA , shipped on dry ice and kept at–20 ºCprior to analysis. Results: the Blastocystis was significantly predominant (P>0.001) parasite associated with IBS which constituted (46.2%). The results of culture were higher than light microscopic examination (48.7%). Individuals with blastocystis infection were found to have positive association with IBS (OR: 73.150 , 95% CI: 9.684-552.531 ). Evaluation of immune status among IBS patients infected with Blastocystis through measuring IL-5 by SandwichELISA, were significantly elevated in the IBS Blasto group (p<0.05) compared to control.