A field experiment was conducted to detect the growth performance of mixed sex Nile tilapia (Oreochromisniloticus) at different stocking density in Danda River, Rupandehi in 1m3 caged culture for 90 days. Theexperiment was conducted in Completely Randomized Design (CRD) with four treatments replicated thrice.The treatments were: Treatment-1, Treatment -2, Treatment-3 and Treatment-4 containing 10, 20, 30 and40 fish/m3 respectively. The mean stocked weight of tilapia fingerling in each treatment was 11.31g, 10.93g,10.23g and 10.10g, respectively. The feed containing 35% CP was supplied at the rate of 5% of body weightin initial month followed by 3% in the latter two months. Fish were fed twice daily at morning 9AM and nextat evening 4PM. In this 90-day study, the study results indicated that Treatment T2 was significantly moreeffective than the other treatments in several key performance metrics (p<0.05). T2 exhibited the highestmean weight gain at 76.32g, significantly greater than T1 (69.83g), T3 (67.80g), and T4 (63.36g). Additionally,T2 recorded the highest daily weight gain at 0.84g, which was significantly greater than the gains in T1(0.77g), T3 (0.75g), and T4 (0.70g). The survival rate in T2 was the highest at 90.00%, while T4 had the lowestsurvival rate at 70.67%, with these differences being statistically significant (p<0.05). In terms of totalproduction, T4 achieved the highest production at 2078.34±22.75g, which was significantly higher than theproduction in T1 (480.48±24.57g) (p<0.05). Although T4 led in gross return at 235.42, the net return washighest in T2 at 61.70, with this being significantly different from the net returns in T1 (9.03) and T4 (2.59)(p<0.05). Additionally, the benefit-cost ratio (BCR) was also highest in T2, significantly outperforming T1, T3,and T4 (p<0.05). These findings suggest that 20 fish/m3 is the most effective treatment for enhancing growthperformance, production, and economic returns in Tilapia fish farming.