A total 2,488 ejaculates during 4 years from 80 Korean native bulls over the age from 3 to 12 years of bull herds of Artificial Breeding Center, National Livestock Federatives Cooperation were collected and analyzed to study the effects of collection year, age of bulls, month of years, collection interval and ejaculation frequency per day on semen volume, sperm concentration, total sperm per ejaculate and sperm motility. 1. Semen volume, sperm concentration, total sperm per ejaculate and sperm motility index for the all ejaculates using least squares procedure averaged 5.73ml, 9.133${ imes}$108/ml, 52.527${ imes}$108 and 62.81, respectively. 2. Semen volume varied significantly with collection year, collection interval and ejaculation frequency per day(P<0.01), but effects of age of bulls and month of years on semen volume were not significant. Eight to 15 days collection interval showed the highest volume, and 1st ejaculate contained 5.6% more volume than 2nd ejaculate. 3. There were significant differences among collection years, months of years and ejeculation frequencies per day except collection intervals in sperm concentration per ml(P<0.05, P<0.01). Six to 8-year-old bulls was the highest concentration. Higher sperm concentration per ml was in April to July and lower month was October and December. Sperm concentration in 2nd ejaculate was higher than in 1st ejaculate. 4. Total sperm per ejaculate affected by all environmental factors studied(P<0.05, P<0.01). Age of bulls, collection interval and ejaculation frequency per day showed the highest total sperm was 6 to 8-year-old bulls, 8 to 15 days interval and 1st ejaculate, respectively. Higher total sperm per ejaculate was in April to July and lower total sperm was in September to December. 5. In sperm motility, there were significant differences among collection years, ages of bulls and collection intervals except months of years and ejaculation frequencies (P<0.01). Higher sperm motility was in 6 to 12-year-old bulls and in 5 to 7 days collection interval.