The soybean [Glycine max (L.) Merr.], an ediblelegume, has a high protein content in both its hay andgrain, so it is often used as a supplement for other foragesthat have a deficient protein concentration. Therefore, thisstudy investigated the forage quality and yield in the caseof mixed planting of soybean and corn. The forage yield andquality were assessed for three cropping patterns: soybeanmono planting, corn mono planting, and mixed planting ofsoybean and corn. For planting, this study used a forage corncultivar, Kwangpyeongok, and three recombinant inbreed lines,W2, W4, and W11, selected from Glycine soja (PI483463)×G. max (Hutcheson). The mixed planting of soybean and cornproduced a higher forage yield than the corn mono cropping.The crude protein and crude fat content were also increasedwith the mixed planting of soybean and corn when comparedwith the corn mono cropping. Some decrease of ADF andNDF, and increase for RFV in mixed planting of soybeanand corn than corn mono cropping. Therefore, the resultsshow that mixed planting of soybean and corn is aneffective cropping system to improve the forage quality.