Bacterial fish diseases are considered as major constraint in aquaculture production. The use of natural phytochemicals is promising in aquaculture because they are safe for the environment and human health, biocompatible and biodegradable. The present study was carried out to investigate the effect of Ocimum basilicum oil on the non-specific immune response of Nile-tilapia (Oreochromis niloticus) and resistance against Aeromonas hydrophila infection. A hundred and eighty Nile-tilapia (Oreochromis niloticus) (20±2 g/fish) were randomly distributed and divided into four equal groups in well prepared glass aquaria supplied with continuous areation. The 1st group was assigned as non-treated control group. The 2nd, 3rd and 4th groups were fed on treated ration with basil oil at concentration of 0.25, 0.5 and 1% of basil oil /kg diet for 42 days, respectively.   The obtained results showed that the orally administrated basil oil has been shown to enhance the non-specific immune response in the treated fish (hematocrit levels, respiratory burst activity, serum lysozyme and serum bactericidal activity) all over the experiment period in compared with the control group. Also, significant decrease in total bacterial count of fish muscles in compared with control group. Mortality rates post challenge infection, were significantly lesser in treated groups in compared with control group. It was observed that the mortalities among the challenged fish are dose related. These findings are supportive of the potential of basil oil use as ecofriendly alternative measures of disease prevention for sustainable aquaculture.