Background: Entamoeba histolytica, Balantidium coli, Giardia lamblia and Blastocystis hominis are most popular invalid parasites in lower gastrointestinal tract of humans in this study in Basra which causing acute enteritis and diarrheal disease in patients.

Objective: Investigate the most important pathogenic parasites in the digestive system of patients coming to the hospitals of Basra province.

Methods: The research under study has been implemented in Dar Alshifaa investment hospitable in Basra Province southern of Iraq, A total of 1050 stool samples collected from patients from less than one month years old to over than 70 years. A direct saline smear preparation was made and examined by light microscopy.

Results: The highest rate of infection was represented by E. histolytica in October 20%, The ratios of G. lamblia, B. colli and B. hominis was 0.57%, 0.38, 0.19 respectively. The infection rate of E. histolytica between 2.7%- 38.46% was registered among children from one day even to ages above of 75 years, the highest infection in age 6 years old (38.46%) and less in children from one day to 3 years (2.7-%- 2.93%). This work was scored highest infection in the males 11.38% while the females was 10.34%. A Pus cells with blood were a common symptom in infection patients.