A total of 375 un-sexed Japanese quail (Coturnix coturnix japonica) chicks, 5 days-old were randomly allotted to 5 experimental groups to examine the effect of the inclusion of rice gluten meal (RGM) at levels of 2.5 and 5% and supplementation of betaine at levels of 0.5 and 1.0 g/kg diet on the growth performance, carcass characteristics, hematology, serum biochemistry and gastrointestinal tract microbiota of growing Japanese quail under summer season. Quails were fed a basal diet and the other four diets contained 2.5 and 5% RGM with 0.5 or 1.0 g betaine supplementation. The results revealed quails fed 5%RGM + 0.5 or 1.0 g betaine achieved the highest (P < 0.05) body weight at 5 weeks of age, quails fed 5%RGM + 0.5 or 1.0 g betaine recorded the highest (P < 0.05) body weight gain at 1–5 weeks of age. Quails fed 5%RGM + 1.0 g betaine improved (P < 0.05) DFI at all periods. 5%RGM + 0.5 or 1.0 g betaine groups recorded the best FCR at 1–5 weeks of age. RGM and betaine improved CP and EE digestibilities. RGM and betaine was lower (P < 0.05) in abdominal fat. Quails fed 5%RGM + 0.5 or 1.0 g betaine increased (P < 0.05) WBC count. HB level of the quails group fed diet contained 5%RGM + 0.5 or 1.0 g betaine was higher (P < 0.05). Betaine supplementation increased (P < 0.05) the lactic acid bacteria count and decreased (P < 0.05) E-coli and coliform counts. In conclusion, the combination of RGM and betaine could maintain the growth performance, intestinal health and improve nutrients digestibility of Japanese quails during summer season.