A b s t r a c t A r t i c l e I n f oThe use of the microalgae Spirulina in aquaculture has several potential advantages over the production of fish. This study was designed to investigate the effect of different replacement levels of fishmeal with Spirulina on some microbiology counts of common carp Cyprinus carpio L., the trail was conducted for 105 days and for this purpose 200 fingerlings common carp had been used. Five experimental diets were used and Spirulina replaced fishmeal protein from the standard diet at0% (T1), 5% (T2), 10% (T3), 15% (T4) and 20% (T5) levels. Psychrophilic count, coliform and Escherichia coli in common carp muscle, intestine and water rearing had been examined in which no psychrophilic bacteria in carp muscles were found as compared to control that were contain 16×10 4 , and the count of coliform bacteria decreased as the ratio of Spirulina increased in the diets, the highest was in control 1.2×10 2 while the lowest was in T3 with 2×10. Different count of psychrophilic bacteria were in common carp intestine; the higher was in the control group with 600×10 4 , while the lowest count obtained in the T5 with 0×10 4 , the same trend had been shown in the coliform counts in fish intestine in which the highest was in T3 with 35×10 2 but the lowest was in T5 with 2×10. The control showed lowest results in psychrophilic count in rearing water with 2×10 and the highest were in other treatments, regarding coliform counts the lowest value had been shown in T2 and T3 (1.5×10 2 and 1.5×102 ) respectively and the highest was in T4 (4×10 2 ).