The current research aimed to reduce the effects of increasing Nile tilapia (Oreochromis niloticus) fish stocking density (SD) as stress factor by using dietary commercial probiotic supplementation (biogen^® or Bactocell^®). The experimental Nile tilapia (mean weight of 4.00 g) were distributed by random into 18 hapa (1.5 X 2 X 2 m), representing to 6 treatments (3 replicates per treatment). In a 2 × 3 factorial arrangement, fish were divided into two main groups. The first group was stocked at 100 fish/m³ and the second was stocked at 150 fish/m³. Each group was divided into 3 sub-groups; the 1^st sub-group was fed on a diet without supplementation with commercial probiotics, the 2^nd and 3^rd sub-groups were fed on diet supplemented with 2 g Biogen and 0.5 g Bactocell/kg diet, respectively. The obtained results showed that all tested water quality measurements were suitable for rearing Nile tilapia fingerlings. With increasing fish stocking density, final body weight (FBW), daily weight gain (DWG), specific growth rate (SGR) and daily feed intake (DFI) of fish significantly (P<0.001) decreased and feed conversion ratio (FCR) significantly (P<0.001) impaired while, survival rate significantly (P<0.001) increased. The highest value for each of (P<0.001) FBW, DWG, SGR and DFI were achieved in fish groups fed diets supplemented with probiotic, while FCR significantly (P<0.001) improved. The interaction between fish SD and dietary probiotic supplementation significantly (P<0.01) affected FBW, DWG and DFI, while SGR and FCR were insignificantly affected. All blood components studied were insignificantly affected with fish SD. Hemoglobin, RBCs, WBCs, total protein, albumin and globulin of Nile tilapia fish significantly (P<0.001) affected with probiotic treatments. The interaction between fish SD and dietary probiotic supplementation significantly (P<0.01) affected WBCs only. Approximate analysis of body composition of Nile tilapia fish showed that, ash percentage only significantly (P<0.05) affected with SD, while crude protein, ether extract and ash percentages were significantly (P<0.001) affected with probiotic treatments. Within low SD the percents relative level of protection (RLP) after the challenge infection test using A. hydrophila in fish groups fed diet supplemented with biogen or bactocell were 100 and 60%, respectively. While, with high SD the RLP was 100 and 75% in fish groups fed diet supplemented with biogen and bactocell, respectively as compared with control fish group in the two levels of SD which recorded 0% of RLP. Final profit margin increased by 30.37 and 10.37%, in fish group stocked at high density and fed diet supplemented with biogen or bactocell, respectively when compared with fish group stocked at low density and fed diet without probiotic. The obtained results recommended that dietary probiotic (biogen or bactocell) supplementation to Nile tilapia (Oreochromis niloticus) diets reduce the effects of increasing stocking density as stress factor and achieve better growth performance, high disease resistance and high margin.