The soybean [Glycine max (L.) Merr.], an edible legume, has a high protein content in both its hay and grain, so it is often used as a supplement for other forages that have a deficient protein concentration. Therefore, this study investigated the forage quality and yield in the case of mixed planting of soybean and corn. The forage yield and quality were assessed for three cropping patterns: soybean mono planting, corn mono planting, and mixed planting of soybean and corn. For planting, this study used a forage corn cultivar, Kwangpyeongok, and three recombinant inbreed lines, W2, W4, and W11, selected from Glycine soja (PI483463)${ imes}$G. max (Hutcheson). The mixed planting of soybean and corn produced a higher forage yield than the corn mono cropping. The crude protein and crude fat content were also increased with the mixed planting of soybean and corn when compared with the corn mono cropping. Some decrease of ADF and NDF, and increase for RFV in mixed planting of soybean and corn than corn mono cropping. Therefore, the results show that mixed planting of soybean and corn is an effective cropping system to improve the forage quality.