The study was carried out  at  Faculty of Agriculture, Ain Shams University to assess the effect of two of algae species (Arthrospira platensis and Nannochloropsis gaditana) on growth performance of monosex  tilapia fish (Oreochromis niloticus), fish were fed on a basal diet supplemented with 0,3,5,7% of each algae. To perform seven experimental treatments were assigned in three replicates each. The experiment was designated as follows:  (T1) control (without algae), (T2) basal diet supplemented with 3% spirulina (spiru 3), (T3) basal diet supplemented with 5% spirulina (spiru 5), (T4) basal diet supplemented with 7% spirulina (spiru 7), (T5) basal diet supplemented with 3% Nannochloropsis (nanno 3), (T6) basal diet supplemented with 5% Nannochloropsis (nanno 5) and (T7) basal diet supplemented with 7% Nannochloropsis  (nanno 7). Experimental tanks were a part of closed recirculating system, where almost constant environmental conditions were kept throughout the experimental period. Twenty-one quadrate fiber glass tanks with 108-liter water capacity were stocked with 15 fish per tank. The individual initial body weight (2.7 g) was recorded at the beginning of the experiment. All fish in each tank was weighed every two weeks during the whole experimental period. The fish were fed the experimental diet for 95 days Results indicated that nanno 5 treatment had higher significant trend (P<0.05) final body weight (FBW), average weight 
gain (AWG) and average daily gain (ADG) compared with the other experimental treatments. The best specific growth rate (SGR), feed conversion ratio (FCR) and feed efficiency ratio (FER) were found in nanno 7. Also, it was observed that spiru 7 have a high significant difference (P<0.05) in protein efficiency ratio (PER) and protein productive value (PPV). On the other hand, the results showed that the lowest AWG, ADG and (FER) appeared in spiru 7%. No mortality in nanno7 and spiru 7. Finally, using of nano 5% or spiru 7% enhance growth performance and feeding in tilapia fish.