This study investigated the effect of Paenibacillus polymyxa LM31 supplementation on growth performance, antioxidative status, immune response, cecal microbiota, and biochemical parameters of growing Japanese quail. Identification of Paenibacillus polymyxa was identified and the volatile organic compounds and antibacterial activity of selected isolate supernatant were determined. A total of 225 unsexed one-wk-old Japanese quail chicks were randomly allocated to 5 treatments (5 pens, 9 birds/pen) and fed either a basal diet as a control group or a basal diet supplemented with four different levels of Paenibacillus polymyxa 0.1, 0.2, 0.3 and 0.4 mg / kg feed. The results of the GC mass profile revealed that several organic compounds were secreted by Paenibacillus polymyxa in the supernatant. The diet supplemented with Paenibacillus polymyxa supernatant showed potent antibacterial properties against gram negative and gram positive bacteria as well as fungi. Paenibacillus polymyxa significantly improved the growth performance of growing quails. Paenibacillus polymyxa administration up to 0.4 mg/kg diet significantly reduced plasma total cholesterol (TC), low density lipoprotein (LDL), very low density lipoprotein (VLDL), and triglycerides (TG). The use of Paenibacillus polymyxa at 0.3 or 0.4 mg/kg diet significantly (P = 0.0042) increased high density lipoprotein (HDL) compared to the control. In addition, dietary supplementation of 0.3 mg Paenibacillus polymyxa /kg diet significantly improved superoxide dismutase (SOD), total antioxidant capacity (TAC), immunoglobulin M (IgM) and Immunoglobulin G (IgG) whereas significantly reduced plasma lipid peroxidation (MDA). Furthermore, Paenibacillus polymyxa administration modulated ceacal microbiota by significantly reducing the count of E. coli and Enterococcus spp. whereas increased lactic acid bacteria. In conclusion, Paenibacillus polymyxa could improve productive performance and body health status of Japanes equail via improving antioxidative status and immune response, increasing the count of beneficial bacteria and reducing E. coli count.