The experiment of this study was carried out for 6 months on rearing Nile tilapia and silver carp, whether under monoculture or polyculture at different stocking densities. Four floating net cages (10 x 10 x 3 m) were used. The obtained results revealed that the best treatment was the monoculture of all males mono-sex  Nile tilapia (10000 fish of 10-g each/cage) followed by that of polyculture (5000 tilapia of 10-g plus 750 carp of 70-g/cage) concerning their superiority in final bodyweight (235 and 545-g/fish), bodyweight gain (225 and 475-g/fish), average daily bodyweight gain (1.21 and 2.55-g), specific growth rate (SGR, 1.70 and 1.01 %/day), feed conversion ratio (FCR, 2.41 and 2.45), feed cost/Kg bodyweight gain (7.78 and 5.89 L.E.), and economic efficiency (144.5 and 77.9%, respectively). Moreover, the monoculture of all males mono-sex  Nile tilapia was also the best treatment in return (18855 L.E./cage) followed by the polyculture treatment (7500 tilapia of 10-g with 1100 carp of 70-g/cage) which gave return of 10868 L.E./cage.