Thirty proven Hanwoo sires, ranging from 5 to 9 years old, were used to investigate the effects of dietary nutrition level, age and body weight on semen characteristics which were analyzed using CASA(Computer-aided sperm analyzer) and to determine the proper nutritive level, age and body weight for production of high quality semen. The groups fed a diet meeting the NRC requirements for maintenance(NRC) had more semen volume than the groups fed at additional 10% level(NRC + 10%). However, tendencies were the opposite in sperm concentration and motion characteristics. Sperm concentrations of 9 years old sires had lower than those of others and the sires below 800㎏ body weight were better than the sires over 800㎏ body weight in sperm motion characteristics[curvilinear velocity(VCL), straight-line velocity(VSL), beat-cross frequency(BCF)] and viability. Although the interaction of age and the nutrition level had not be significant on semen characteristics, VCL, VSL and ALH(amplitude of lateral head displacement) of the groups fed at NRC + 10% were better than those of the grops fed at NRC in every age. The sperm concentration of 9 years old sires with below 800kg of body weight were the lowest. The sperm motion characteristics of 7-8 and 9 years old were best in below 700㎏ and over 700㎏ of body weight, respectively. But individual difference of sperm motion characteristics were large in 9 years old sires. In every body weight except 700∼800㎏, the semen characteristics of groups fed at NRC + 10% were better than the those of groups fed at NRC. But the semen characteristics of the group of 700∼800㎏ body weight fed at NRC was the best among the those of others. Therefore, the proper age and body weight of Hanwoo sire for production of high quality semen would be 5∼8 years old with below 800㎏ of body weight. Feeding plane of sire below and over 700㎏ body weight would be fed at NRC + 10% level and NRC, respectively.