The objectives of this study were to determine by experimental results the age at first calving, gestation length and calving interval of Jeju native, Brahman, Santa Gertrudis and crossbreeds. Data were analysed by the least square method, from 582 cows fed at Jeju Experiment Station from 1961-1980. 1. The average age at first calving of Jeju native, Brahman and Santa Gertrudis was 41.9, 42.8 and 39.8 months respectively. The average age at first calving of Brahman × Jeju native and Santa Gertrudis was 39.1 and 42.1 months. 2. The average gestation length of Jeju native, Brahman and Santa Gertrudis was 285.9, 286.2 and 284.7 days respectively. The average crossbreeds gestation length, however, was longer than their parents with an increase of 1% in Brahman × Jeju native and 4% with Santa Gertrudis × Jeju native cattle. 3. The average calving interval of Jeju native, Brahman and Santa Gertrudis was 384.7, 465.9 and 501 days. Crossbreeds, however, have shorter calving intervals than their parents with an increase of 5.3% in the case of Brahman × Jeju native and 6.4% with Santa Gertrudis × Jeju native cattle (P$lt;0.01). 4. Gestation length was longest when dam was 8-9 years old (P$lt;0.05) but calving interval declined as parity increased.