Age at puberty has become a key trait in the genetic evaluation of female reproduction traits for tropically adapted beef breeds in northern Australia. This study aimed to characterise the trait in Australian Hereford seedstock heifers and to determine the degree to which it, and associated traits, were under genetic control. Hereford heifers (n = 922) from three seedstock herds were serially ultrasound scanned to detect their first corpus luteum (indicative of age at puberty) at 4 - 6 week intervals from 10.6 to 13.2 months of age, at which time heifers were synchronised for artificial insemination. Results showed that only 52% of heifers were pubertal at synchronisation, and for these heifers, age at puberty had a heritability of 0.26. When a penalised record (equal to the maximum age at puberty for their contemporary group plus 21 days) was included for heifers which were not pubertal into mating, heritability increased to 0.38. For sires with at least 10 progeny, EBVs for age at puberty ranged from -42 to 28 days. The ability of heifers to conceive early in their first mating season is linked to lifetime reproductive performance. These results suggest that the proportion which have reached sexual maturity as they enter their first mating is significantly less than 100% and that opportunities exist, if the trait were included in the genetic evaluation for the breed, to monitor and apply selection to improve age at puberty in Hereford heifers.