This experiment was conducted to find out the most suitable seeding rate and N fertilization level for maximum green forage yield in a double-cropping system of sorghum×sudangrass hybrid(Sorghum bicolor L.) and winter rye(Secale cereale L.) from April, 1992 to May 1993. As the principal crop, sorghum×sudangrass hybrid was planted at 3 levels(100, 200, 300 ㎏/㏊) of N fertilization with 2 rates (80. 110 ㎏/㏊) of seeding. After third harvest of the principal crop, winter rye, as the second crop, was planted in a similar way(100, 160, 220 ㎏/㏊ of N fertilization and 150, 200㎏/㏊ of seeding rate). The contents of CP, ADF and NDF, and IVDMD of the principal and second crops showed little change with the different seeding rates and N fertilization rates. DM yield of sorghum×sudangrass hybrid was increased with the higher seeding rate(P$lt;0.05) and that of winter rye was increased with higher N fertilization. DM yield of sorghum×sudangrass hybrid was 14,845㎏/㏊ at 100㎏/㏊ of N fertilization with a 110㎏/㏊ seeding rate and that of winter rye was 9,881㎏/㏊ at 220㎏/㏊ of N fertilization with a 200㎏/㏊ seeding rate. Therefore, to achieve maximum double-cropping yields, sorghum×sudangrass hybrid should he planted with 110㎏/㏊ of N at 110㎏/㏊ seeding rate and winter rye should be grown with ?20㎏/㏊ of N at a 200㎏/㏊ seeding rate.