Abstract: The present study included species composition of fish and some ecological factors in haji Ali drainage in the Babylon province. Three stations were chosen for the purpose of the study, the station of first is placed at the beginning of the drain(St1), the second in the middle(St2) and the third at the end(St3), monthly samples were selected from June 2019 to May 2020. Water temperature showed slight changes to the stations were recorded between(11.8C°-28.9C°).Salinity ranged between 0.12gm/l -2.55 gm/l. pH values tended in some months of study to the acidic side and in other months to the basic side has recorded from (6.4-9.3). Dissolved oxygen values ranged from (1.71- .86)mg/l.Biological oxygen demand values ranged between (0.04-4.59) mg/l.Throughout 8 fish were obtained, belonging to 14 species 397of 5 the period mentioned above, a total and 7 families, 11 species of them were native species whereas 3 of them were alien species. The most abundant species was Carassius auratus constituted 31.28% of the total caught of the first station, the value of the dominance index (D3) in first station was 78.53%. The most abundant species in second station was C. auratus constituted 31.46% of the total caught, the value of the dominance index (D3) in the second station was 70.03%. The most abundant species in third station was Planiliza abu constituted 28.08% of the total caught, the index of dominance value (D3) in the third station was 75.68%. Richness index (D) was ranged between (0.66-1.92) and diversity index (H) recorded (1.07-2.01),while evenness index (J) ranged (0.55-0.70).