In order to study on the development of the spermatogenic function and the sexual maturity between the Korean purebred and three-way crossbred ((Angus × Korean purebred) × Holstein), this experiment was conducted to investigate the testicular development and the spermatogenetic function by means of repeating biopsy at one month intervals from one to 9 months of age with 6 Korean purebreds and 3 three-way crossbreds. 1. In the testicular development, the scrotum circumference of the Korean purebred and three-way crossbred increased steadily with increasing age. The scrotum circumferences of the Korean purebred and three-way crossbred were 19.4 ㎝ and 28.9 ㎝ at 9 months of age, respectively, and doubled to one month of age. The testicular width and length increased rapidly from 6-7 months of age, but the differences between two groups were not statistically significant. 2. The seminiferous tubules in the testis of two groups, solid at 3 months of age, increased appearently in diameter at 5 to 6 months of age, but were not reached mature size. 3. Only gonocytes and indifferent supporting cells were present in the tubules at 3 months of age and spermatogonia appeared from 5 months of age, spermatocytes increased rapidly from 6 months of age and spermatid were seen for the first time in the 7 months old Korean purebred and three-way crossbred. On the basis of the above results it is concluded that sexual maturity of three-way cross bulls was somewhat earlier than the Korean bulls, but the difference of two groups was not significant.