There exists conflicting reports concerning the influence of supplemental herbs or essential oils on blood biochemical profile. It was reported that using 2% blends of ziziphora, menta, peppermint and nettle did not affect blood biochemicals in laying hens (Sayedpiran et al., 2011), and diet supplemented with 36 mg/kg essential oils had no effect on serum total cholesterol of laying hens (Özek et al., 2011). And serum calcium concentration was significantly decreased by dietary supplementation of bergamot oil (1.5 ml/kg) to laying hens during the late laying period (75 week old) (Bölükbas¸ i et al.,2010). For clear conclusion, further systematic studies might be considered to elucidate the effect of peppermint leaves at different stages of production in laying hens