This study aimed to evaluate the impact of betaine (Bet) and protected calcium butyrate (PCB) supplementation individually and together on the performance, carcass traits, blood biochemistry, and meat quality of growing Japanese quails (Coturnix coturnix Japonica) from 1 to 42 days old. 144 one-day-old unsexed Japanese quails were randomly assigned to four dietary treatments with six replicates each. All birds were fed a maize-soybean meal diet for 42 days. The control group received no feed additives, while the treatment groups received 1.2 g/kg Bet, 1.0 g/kg PCB, or a combination of both in their diets. The results indicated that Bet and PCB supplementation individually and together did not differ performance, relative weights of heart, gizzard, proventriculus, bursa of Fabricius and pancreas, water holding capacity (WHC), cooking loss (CL), blood biochemical values except for glucose and triglyceride. Bet supplementation significantly increased relative liver weights, while PCB supplementation decreased glucose levels in serum. Moreover, carcass yield was increased and triglyceride value in blood serum, malondialdehyde (MDA), and the pH levels of breast meats both on the 1st and 30st day of post-mortem were decreased in all treatment groups. Therefore, based on these results, the combination of betaine and butyrate improves both carcass yield and meat quality in growing Japanese quails. More research is needed to determine the impact of betaine and butyrate on the structure of amino acids in meat, antioxidant enzyme activity, and the immune system in poultry.