Effects of Mentha piperita (peppermint) extract and juice on performance and immune parameters were evaluated in laying hens. A total of 252 Babcock laying hens were allocated to seven treatments with four replications of nine hens. The control hens were fed a basal diet without supplementation. Other hens were given diets supplemented with mentha extract (ME) at 50 (50ME), 100 (100ME), and 200 (200ME) mg/kg of feed or with 50 mentha juice (50MJ), 100 (100MJ) and 200 (200MJ) mg/L that was provided in the drinking water. No significant differences were detected among treatments in bodyweight, feed intake, egg mass, egg production, eggshell breaking strength, Haugh unit, and haematological and serological parameters. The ratio of gram feed to gram egg mass (feed conversion) was significantly better in the birds that received 100ME and 200ME compared with the control hens. The yolk colour index was higher in mid trial analysis (28th day). Thus, although the ME supplementation had a positive effect on feed conversion ratio and egg yolk colour at dosage rates up to 200 mg/kg, further research is needed to establish the efficacy of this herbal product and to determine the most appropriate amount to include in diets for laying hens.