This study was conducted in the cold storage unite in the Dept. of Hort., College of Agric., University of Baghdad starting in 20/ 1/ 2009. The white strain of oyster mushroom was imported from Jordan. The spawn was grown on wheat seeds. Wheat straw was used as substrate. Commercial formaldehyde 2% was used for sterilization of the straw. Plastic bags (30 X 51 cm) was used and 1 kg of moist substrate in each bag used for spawning. The bags were transfered to the incubation room at 25 ± 2ْ c for one month then to the growth room. Humidifier was used to raise the humidity to 80-90% and fluorescence lamps were used to raise light to 400 Lux. Water extract of liquorice roots (Glycyrrhiza glabra) was used with the following concentration: 0% , 5% , 10% , 15% and 20%. The extract was injected (30ml.) inside the plastic bags using 50 ml. syringe. Injection was done during three stages of growth. The first injection was in the middle of the incubation stage and the second injection was in the begning of the Pinhead stage and the third injection was in the begning of the fruiting body stage. The results showed that treatments with Liquorice root extract during the three stages significantly increased fruiting body weight and total yield and dry yield and the biological efficiency of oyster mushroom. Treatments also reduced the production cycle and increased the percentage of dry matter, and increased the percentage of protein content of the fruiting body. Storage life of the oyster mushroom was improved because of the reduction of weight loss and dry matter loss and protein loss during 15 days of storage at 2 ±1ْ c. Treatments with liquoric extract in the begging of the fruiting body stage reduced the percentage of decay during cold storage. The results of this study showed that the best growing stage for liquorice extract treatment was the beging of fruiting body stage and the best concentration was 20%. Treating oyster mushroom with 20% Liquorice extract in the begging of the fruiting body stage increased fruiting body weight to 15.98 g and increased total yield to 852.8 g/kg of substrate and increased the dry yield to 115.42 g/kg of substrate and increased the biological efficiency to 85.3%.