Tilapia is one of the most important farmed fish in the world. The main objective of this study was to evaluate the effects of supplementation the graded levels (0, 5, 10, and 15 g / kg diet) of a new commercial probiotic Hydroyeast Aquaculture^® to low crude protein (CP) levels (20 and 25%) in diets of male monosex Oreochromis niloticus fingerlings for 14 weeks, regarding their growth performance, feed utilization, carcass composition, hematological, and histometeric parameters of the intestine. Fish with an average initial body weight (7.5 ± 0.001 g) were distributed into eight treatments (three replicates per treatment). Fish in each treatment were stoked at 5 fish / aquaria (90×40×35 cm).The results revealed that the high levels of CP (25%) and probiotic (15 g / kg diet)had positive significant (P ≤ 0.05) effects on fish growth performance parameters, feed utilization, fish carcass composition (DM, CP, and EC), hematological constituents (hemoglobin, red blood cells, packed cell volume, and blood platelets) and intestine histometric parameters compared with other treatments, but the interaction between them was not significantly affected on all the above parameters. Therefore, it could be concluded that the high level of probiotic 15 g Hydroyeast Aquaculture^® / kg diet is useful with low dietary CP level (25%) in feeding fish at early age stage for enhancing the production performance, physiological responses and histometeric parameters of the intestine of male monosex O. niloticus fingerlings, thus this level of probiotic may lead to increase the economic efficiency at large scale in the fish farms.