A natural feed of fresh seaweed and sixteen diets designed by L16 (4³) orthogonal array were formulated to contain different levels of protein (200, 250, 300, and 350 g/kg), vitamin E (VE) (0, 0.1, 0.3, and 0.5 g/kg), and vitamin C (VC) (0, 0.5, 1, and 1.5 g/kg) to evaluate the effects of dietary protein, VE, VC, and their combination on growth and gonadal development of hybrid male abalone (Haliotis fulgens ♂ × H. discus hannai ♀). Each diet was randomly assigned to triplicate groups of 18 abalones (34.27 ± 2.93 g) that were stocked in sea cages for 8 weeks. Results showed that the maximum weight gain (WG) and specific growth rate (SGR) were obtained in hybrid male abalone fed D10 diets. The highest gonad somatic index (GSI) value was found in the D14 diet. Moreover, the ANOVA results showed that only dietary protein could significantly affect the GSI of hybrid male abalones (P < 0.05). A significant difference was observed among the groups in terms of total protein, total cholesterol, triglyceride, acid phosphatase, and alkaline phosphatase (P < 0.05). The mRNA expression of vasa in the testis of D14 abalone was the lowest. Abalones fed the D14 diet had higher testosterone levels and sperm in the testis than those fed other diets. In conclusion, protein of 300 g/kg, VE of 0.1 g/kg, and VC of 1.5 g/kg (D10) and protein of 350 g/kg, VE of 0.1 g/kg, and VC of 1 g/kg (D14) might be the optimal combinations in the diet for growth and gonadal development of hybrid male abalones respectively.