This study was performed to study the impacts of rosemary cold-pressed oil (RCPO) for biostimulating health, growth performance, and intestinal bacterial populations of Japanese quail. The study included 300 growing 1-wk-old Japanese quails. Birds were divided into 3 groups in a complete randomized design experiment that involved 3 levels of RCPO (0, 1.00 and 2.00 mL/kg diet). Results revealed that the addition of rosemary oil numerically increased values of body weight and body weight gain when compared with the control group, particularly the highest level of RCPO (2.00 mL/kg diet). Birds fed diets supplemented with rosemary oil consumed more feed (P ≤ 0.01) compared with those fed the control diet. Feed conversion ratio tended to be improved in rosemary oil groups during the period 3 to 6 wk of age (P = 0.013). The highest level of rosemary oil (2.00 mL/kg diet) had the best impact on all carcass traits studied. RCPO supplementation showed an increase in serum total protein, metabolic hormones levels, while it reduced serum cholesterol and low-density lipoprotein cholesterol, 8-hydroxy-2′-deoxyguanosine, and protein carbonyl levels. Moreover, RCPO increased antioxidative enzymes, and reduced the lipid peroxidation in quail liver. The supplementation of 2 mL/RCPO kg diet showed significant reduction in populations of total cultural bacterial count, coliforms, Escherichia coli, and Salmonella spp. in the ileum when compared to the control. The current results showed that RCPO supplementation to Japanese quails diet could enhance the growth performance and reduce the intestinal pathogenic bacteria. Therefore, RCPO can be a beneficial antimicrobial and growth-promoting feed supplement for the Japanese quail.