The present research work was conducted to evaluate the effect of phytase supplementation on growth and nutrient digestibility of the Catla catla fingerlings fed Moringa by-products based diets. The existence of phytic acid in plant by-products decreases the bioavailability of minerals and nutrients to fish, resulting in poor fish growth and low nutrient retention in the body. Moringa by-products such as Moringa oleifera leaf meal (MOLM), M. oleifera seed meal (MOSM) and a mixture of MOLM+MOSM were used as test ingredients to formulate three experimental diets. Each experimental diet was further divided into six groups and were supplemented with graded levels (0, 300, 600, 900, 1200 and 1500 FTU kg-1) of phytase. Cr2O3 was incorporated in all diets at the rate of 1% as a non-digestible marker. The fingerlings were fed at the rate of 4% of live wet weight twice a day and faeces were collected from each tank. On the basis of results it was noted that phytase supplementation showed significant (p<0.05) improvement in growth indices (weight gain%, FCR, SGR), digestibility of nutrients (i.e. crude fat, crude protein and gross energy), mineral absorption, carcass composition and haematological parameters. Results showed that maximum absorption of minerals, nutrient digestibility, higher body contents (protein, fat and gross energy) and best haematological parameters of C. catla fingerlings were noted at 900 FTU kg-1 level of phytase supplemented M. oleifera by-products based test diets. It was further noted that phytase supplementation decreased the discharge of nutrients and minerals through faeces resulting in reduced aquatic pollution. On the basis of results it was concluded that phytase supplementation at 900 FTU kg-1 level was helpful to develop a cost-effective as well as eco-friendly fish feed by using Moringa by-products. Furthermore comparison of Moringa by-products suggested that phytase supplemented MOSM performed as a better alternative protein source for C. catla fingerlings than the other MOLM and MOLM+MOSM ingredients based diets.