Commonly known as the button mushroom, Agaricus bisporus is one of the most widely cultivated mushroomspecies of edible fungi. In the breeding of new button mushroom, Seolwon was developed by crossing two homokaryons.Because of the predominantly pseudohomothallic life cycle, only a small percentage of homokaryotic meiospores are produced,which do not fruit. Homokaryotic cultures derived from these types of single spores produce a vegetative mycelium that contain avariable number of genetically identical nuclei per cell. After crossing two homokaryons, hybrids were cultivated on a small scaleand on a commercial scale at a farm. The spawn was made by a commercial spawn producer and the spawned compost by acommercial compost producer. Mycelial growth of Seolwon on CDA was better at 25oC when it was compared with that ofSeolgang. The mature cap shape of new strain Seolwon is oblate spheroid and the immature cap shape is round to oblatespheroid. The cap diameter was 39.7 mm on average. In comparison with white strain Seolgang, the strain had a yield that was11% higher. It produced fruiting bodies which had a higher weight on average per fruiting body and were 9.7% firmer with agood shelf life. Days of fruiting body were 1-2 days later than those of Seolgang. The physical characteristics such as springiness,chewiness, adhesiveness, gumminess were better than that of Seolgang.