This study was carried to investigate suitable additive materials and its mixing ratio in pot cultivation of Pleurotus ostreatus. The main substrate for Pleurotus ostreatus cultivation was poplar sawdust plus with waste cotton at the ratio 1 : 1 (v/v). Using pot diameter and substrate weight were 12 cm and 1 kg/pot, respectively. The higher amount of additives resulted in higher total nitrogen content and C/N ratio of substrate also decreased according to increasing mixing ratio of additives. The supplementation of cotton seed flour more than 20% caused the failure of devolopment of fruit body. The hardness of substrate in supplementation of rice bran after mycelial growth was highest any other additives. The ratio of harvest was highest in supplementation of beet pulp, $75{sim}85%$. The fruit bodies yield and biological efficiency of supplemented with 20% beet pulp were highest during second flush.