A total number of two hundreds (200) naturally infected and freshly caught Oreochromis niloticus were collected randomly and seasonally from western lagoon (abranch from Lake Temsah in Ismailia governorate). The clinical picture of septicemia in the affected O. niloticus were observed and examined to isolate and identify the bacteria causing motile aeromonas septicemia. The most isolated bacteria was Aeromonas sobria which identified by using traditional methods and Vitek 2 system. Also confirmed by detection of 16s rRNA gene using PCR. The virulence of A. sobria was determined by detection of hemolytic activity on blood agar and hemolysin gene using PCR. The total prevalence of A. sobria in O. niloticus was 63%, with the highest prevalence in summer (92%) followed by spring (80%) then autumn (60%) while the lowest prevalence was in winter (20%). A. sobria was isolated with high prevalence from kidneys, liver, spleen and intestines at rates of 25.39, 23.02, 19.84  and 15.08 % respectively. The lowest prevalence was recorded from gills and skin lesions as 10.32 and 6.35 % respectively. The experimentally infected O. niloticus by (I/P) showed the same picture recorded in the naturally infected fish. The mortality rate and reisolation of the injected bacteria were tried and recorded.