Abstract: This study was undertaken to evaluate the quantitative requirement of dietary ascorbic acid supplementation in the diet of African catfish, Clarias gariepinus, using growth performance, nutrient utilization. Clarias gariepinus fingerlings weighing 6.02±0.4 g were randomly distributed into glass tanks of 60x45x45 cm³ dimension at ten fish per tank in a triplicate treatment. Five isonitrogenous and isocalorific diets containing 40% crude protein was formulated. Ascorbic Acid (AA) was supplemented in the diets as ascorbyl-2-polyphosphate. Each treatment had varying levels of Ascorbic Acid (AA) supplementation, at 0 (Control) 50, 100, 150 and 200 mg AA kg^-1, in Treatment 1, 2, 3, 4 and 5, respectively. Fish were fed practical diets twice daily at 900 and 1600 h. Weekly weighing of fish was done and the data collected were subjected to statistical analysis. Biological evaluation of the fish was based on growth performance and nutrient utilization efficiencies. At the end of week 4, fish fed scorbutic diets (diets without Ascorbic acid supplementation) had significantly lower weight than fish fed AA supplemented diets (p<0.05). The results showed that the productivity indices, mean Body Weight Gain (BWG), Specific Growth Rate (SGR), Feed Conversion Ratio (FCR), Protein Efficiency Ratio (PER) and Feed Efficiency Ratio (FER) in all the treatment were significantly different from each other at (p<0.05). The best Feed Conversion Ratio (FCR) was recorded in treatment four as 0.94.±0.08 and the poorest FCR was obtained in treatment 1 (Control) fed scorbutic diet as 1.77±1.20. In all parameters considered, treatment 4 fed 150 mg AA kg^-1 gave the best growth performance and nutrient utilization efficiencies, while treatment 3 fed 100 mg AA kg^-1 showed the minimum dietary AA supplementation that prevented growth reduction in this study.