The button mushroom, Agaricus bisporus, is one of the most widely cultivated mushrooms. The domestic production of cultivated mushrooms in 2016 was approximately 10,173 tons, with a total value of 59 billion won. Currently, 10 cultivars have been developed; however, Korean farmers continue to demand new cultivars of mushrooms with improved quality. To breed superior lines, KMCC00754 and KMCC00775 were selected as mother strains from the 170 collected genetic resources. The putative homokaryotic strains were 25 strains from the 120 SSIs of KMCC00754 and six strains from the 120 SSIs of KMCC00775 selected by using the AbSSR45 marker. These homokaryotic strains were crossed with each other and the crossing was confirmed by SSR analysis. Seventy-four lines were crossed into 150 lines for a 50% ratio of crossing. Abs2-2015-16 was selected as a superior line by three cultivations. A new cultivar, ‘Dodam’, was developed in 2017.