A 45-day feeding experiment was conducted to examine the effect of dietary ascorbic acid (AA) supplementation on the growth of milkfish larvae. Five isonitrogenous and isolipidic (580 g protein/kg and 120 g lipid/kg) experimental diets were prepared with varying levels of AA supplementation at 0 (AA0), 250 (AA250), 500 (AA500), 1000 (AA1000), and 2000 (AA2000) mg ascorbic acid (L‐ascorbyl‐2‐polyphosphate) equivalent/kg diet. The experiment results revealed that milkfish fed with 500 and 1000 mg/kg of AA showed significantly better (p < 0.05) performance in terms of final body weight, weight gain, specific growth rate and survival rate. The highest level of red blood cells count in pre- and post-challenge groups was recorded in AA500 group. Intestinal histology revealed that the length of villi, the thickness of lamina propria, and the concentration of lymphoid cells in the lamina propria were observed to be more in AA500 and AA1000 compared with control, AA250 and AA2000. AA supplementation at 1000 level (AA1000) had the best survival (93.3%) against Vibrio harveyi challenge (5 × 105 CFU/fish) with significantly higher survival compared with control. Based on the curvilinear (polynomial) regression analyses, the optimum final body weight, weight gain, specific growth rate, feed efficiency ratio, protein efficiency ratio, and survival were obtained at dietary ascorbic acid levels of 1175, 1174, 1238, 1262, 1246 and 1174 mg/kg diet, respectively. Accordingly, the optimum dietary ascorbic acid required for milkfish in a range of 1174 mg/kg to 1262 mg/kg is beneficial for better health, survival, and growth. The findings of this study can be used as the baseline scientific information on the ascorbic acid requirement for the formulation of a cost‐effective diet for milkfish larvae.