Abstract A feeding trial was conducted to evaluate the effects of plant extracts derived from Mentha arvensis (MA) and Geranium thunbergii (GT) on broiler performance, carcass yield, digestive organ weights, meat quality and odorous gas emissions from the excreta. A total of 210 one-day-old broiler chicks were randomly assigned to one of the following dietary treatments for five weeks: (1) control, (2) 0.1% MA, (3) 0.05% GT, (4) 0.1% GT and 0.1% mixed preparation with varying ratios such as (5) 0.1% 1MA:1GT, (6) 0.1% 1MA:4GT and (7) 0.1% 4MA:1GT. The weight gain (0–3 weeks) was significantly (P<0.01) increased in response to dietary inclusion of plant extracts; however, no significant differences were observed in breast and thigh meat yield (P>0.05). Additionally, no differences were observed in proventriculus, gizzard, pancreas, small and large intestine weight. When compared with the control group, birds fed plant extracts had the lowest meat TBARS value after 0 and 3 weeks of storage (P<0.05). Moreover, the pH value was significantly lower (P<0.05) in the plant extract supplemented groups at 0 weeks. The faecal H₂S emissions were significantly reduced at 0 h and 6 h in all supplemented groups relative to the control (P<0.05). Similarly, NH₃ emissions were reduced at 0 h and 6 h for all supplemented groups except the 0.1% 1MA:1GT group (P<0.05). Overall, the results of the present study indicate that plant extracts supplementation can be used to improve performance and meat quality of broiler chickens while reducing the emission of harmful gases from the excreta.