Four groups ( 45 fish each ) of Orechromis niloticus were used to investigate the efficacy of oral and intraperitoneal vaccination with a polyvalent vaccine prepared from A. hydrophila, and A. veronoo against Motile Aeromonas Septicemia. Group (1) was fed with the bacterin at a ratio of 200 mg wet cell / kg fish body weight for 12 weeks daily a ratio of 3% feed of fish body weight. Group (2) was control oral. Group (3) was intraperitoneally (I/P) vaccinated with 0.1 ml contraining 9 * 10^9 cells / ml of the vaccine preparation at zero day and another booster dose at 8th week. Group (4) was injected intraperitaneally with 0.1 / ml of Freunds incomplete adjuvant at zero and 8th week. Fish immunized either orally or interaperitoneally had ahigh level of serum antibodies against A. hydrophila, and A. veronii if compared with controls throughout the experimental period ( 12 weeks ). After challenge with A. hydrophila, in relation to control group, or A. veronii, both groups of immunized fish had a lower mortality % and a higher relative level of protection (RLP). It is clear that I/P route of vaccination had RLP higher than oral route of vaccination throughout the experiment period. Re - isolation and identification of A. hydrophila and A. veronii were done from the anterior kidney of challenged fish with both organisms.