Abstract The current study investigated the effects of supplementing the diet with chilli pepper ( Capsicum frutescens Linn.) powder on productive performance, carcass traits and faecal pathogenic bacteria population of Japanese quails. The experiment was executed in a Completely Randomised Design (CRD). After being weighed, 180 male Japanese quails that were 3 weeks old were then randomly divided into 3 treatment groups with 4 replicates of 15 birds each. Commercial feed was used as the control group for the quails in T1; 10 g/kg chilli pepper powder was supplemented to T2, and 20 g/kg chilli pepper powder was added to T3. The results found that adding chilli pepper powder at 10 g/kg and 20 g/kg significantly increased (P<0.05) feed intake and final body weight. The live body weight, dressing weight, eviscerated weight, carcass percentage, breast percentage and liver percentage of Japanese quails increased dramatically when 10 g/kg and 20 g/kg of chilli pepper powder were added to their diet. Quails fed a diet containing 20 g/kg of chilli pepper powder had a higher percentage of testicles but a significantly lower percentage of abdominal fat. Additionally, supplementing the diet with 20 g/kg chilli pepper powder considerably decreased (P<0.01) Escherichia coli (E. coli) and Salmonella spp. (P<0.01) in faeces. In conclusion, supplementing the diet with 20 g/kg of chilli pepper powder may enhance productive performance, carcass traits and reduce faecal pathogenic bacteria in 9-week-old Japanese quails.