The effect of inorganic fertilizers with different N:P:K ratios was investigated. Eight earthen ponds (surface area 155 m²) were used in this study. Each pond was stocked with 150 fish of Nile tilapia; Oreoch­romis niloticus (10-15 kg/fish). The ponds received inorganic fertilizer with ratios of 20:20:5, 20:40:5, 40:20:5 and 20:20:0 N:P:K at a rate of 40 kg/feddan/month. The obtained results revealed that there were no significant differences in water temperature, dissolved oxygen, pH value, free ammonia, total alkalinity, total hardness, nitrate and total nitrogen during the effect of different N:P:K ratios. Only, Secchi disk reading, wa­ter conductivity and orthophosphate concentration were significantly af­fected by the applied treatments. The mean values of chlorophyll 'a' content over all the rearing period showed non-significant difference. The optimum production of Nile tilapia was obtained at the ratio of 20:20:5. Data of carcass proximate analysis showed that there were no significant differences in dry matter, crude protein and ash contents of different N:P:K ratios, while, the highest lipid content was obtained at 20:20:5.