A 12- week feeding trial was conducted to examine the effects of dietary zeolite and stocking density on the performance of mono-sex Nile tilapia, (Oreochromis niloticus) fries reared in hapas. Diets supplemented with different levels of natural zeolite (0, 15 and 30 g/kg diet), defined as CTRL, Z15 and Z30. The initial weight of fish was (1.75±0.02 g) and were randomly distributed in 18 hapas (1.5 × 0.5 × 1.0 m3) located in six concrete tanks (2 × 2 × 1 m3) under two levels of stocking density (20 and/or 40 fries/hapa). The diets used in the trial were designed to be comparable in crude protein (30.8 ± 0.2%) and crude lipids (5.04 ± 0.06%). The obtained results showed significant interaction between zeolite level and stocking density for temperature, dissolved oxygen, pH and ammonia concentrations in the rearing water. A significant increase in final body weight (FBW), weight gain (WG), average daily gain (ADG) and specific growth rate (SGR) was found and fish fed a diet supplemented with 30 g /kg of zeolite (Z30) in the high stocking density (40 fish/hapa) had the best feed conversion ratio (FCR) in comparison with the other groups, while a significant decreasing trend was observed in the survival rate by increasing the dietary zeolite level. Furthermore, notable variations were noted in feed consumption between fish fed diets varied in amount of dietary zeolite. In terms of, protein efficiency ratio (PER) results showed that fish fed Z30 diet in the high stocking density significantly differed among all treatments and followed by fish fed CTRL diet in the low stocking density. The outcomes of body composition examination revealed that the lowest dry matter was in fish fed CRTL diet without zeolite supplementation and more significance differences were observed in the interaction effect between dietary zeolite and stocking density in terms of protein content. Ash content values were increased by increasing the dietary zeolite level with significant differences. The least amount of lipids was found in fish fed Z30 diet under the high stocking density (40 fish/hapa). These findings led us to the conclusion that natural zeolite can be added to the diets at 30 g/kg under high stocking density (40 fries/hapa) and may improve the efficacy of mono-sex Nile tilapia fries reared in hapas.