Abstract: Background and Objective: The melon fly, Bactrocera cucurbitae is a very serious pest of fleshy fruits and vegetables in Bangladesh. Damage levels can be reached up to 100% of unguarded cucurbit crops. The impact of milk protein casein hydrolysate as additive to adult diet on the biological parameters of B. cucurbitae was studied. The objective of this study was to examine the effects of 2 artificial adult diets on different biological parameters of B. cucurbitae. Materials and Methods: Experiments were conducted by using same sizes of adult rearing cages fencing with nylon net. Two different diets (Yeast extract: Sugar, 1:3 as Diet1 and Casein hydrolysate: Yeast extract: Sugar, 1:1:3 as Diet2) were served as adult food source and tap water with soaked cotton as water. Sweet gourd was given as egg laying and larval food medium. Results: Mean egg incubation period was 2.33 days in both diets. Larvae and pupae of D2 took slightly higher duration than D1. Adult emergence% and male-female ratio indicate a positive correlation to D1 though a slightly higher population of overall adult and female produced in D2 in F1. Pupae and their weight also indicate a better result in D1. Results showed no significant differences for egg incubation period, larval duration, pupal period, pupae recovery, adult emergence and sex ratio of B. cucurbitae, reared on 2 different adult diets. It indicates that casein hydrolysate as milk protein additive had no remarkable effect on different biological parameters of the melon fly, B. cucurbitae. Conclusion: Results revealed that yeast extract and sugar (1:3) diet (D1) was most suitable for the development of melon fly in sterile insect technique under laboratory condition.