Earthen ponds (surface area 155 m² each) were used to study the effect of different doses of inorganic fertilizer on water quality and fish production. Each pond was stocked with 150 fish of Nile tilapia; Ore­ochromis niloticus (25-30 gifish). The ponds received inorganic fertilizer (20:20:5 N:P:K) with doses of 0, 20, 40, 60 and 100 kg/fed/mth. The obtained results revealed that there were no significant differences in water temperature, dissolved oxygen, pH value, free ammonia water con­ductivity, nitrate concentration, total hardness, and total alkalinity due to the effect of different doses of inorganic fertilizer. Only Secchi disk reading, orthophosphate concentration and total nitrogen were signifi­cantly affected by treatments. Chlorophyll 'a' content over all the rear­ing period was increased by increasing the applied doses and the highest one was obtained with using 100 kg/fedirnth. The optimum production of Nile tilapia was obtained with the dose of 60 kglfed/mth. Data of car­cass proximate analysis showed that there were no significant differenc­es in dry matter, while crude protein total lipids and ash contents dif­fered significantly by different doses.