All bears give birth to highly altricial young, but maternal style is markedly divergent among species. Like many aspects of sun bear (Helarctos malayanus) life history, maternal care in this species is poorly documented. Using detailed systematic behavioral observations, we provide the first quantitative report on the mother–cub relationship and early behavioral development in a sun bear. We summarize temporal changes in mother–cub behavior as the cub ages and evaluate maternal investment in the cub. We also provide developmental milestones documented in 2 cubs born (one in 2004, one in 2006) at the San Diego Zoo and compare them with those available in the literature. This sun bear mother displayed behavior indicating a high level of behavioral investment in young offspring while still in the den. She held the cub off the ground, cradled it to reduce the cub's exposure to ambient air, and was attentive to the cub's needs, responding to nearly 50% of the cub's vocalizations and grooming the cub frequently. We conclude that the maternal care behavior of sun bears appears to be active, comparable to the giant panda (Ailuropoda melanoleuca) and different from the more passive maternal care displayed by American black (Ursus americanus) and brown bears (U. arctos) during the denning phase. A growing number of studies of maternal care in ursids are beginning to provide insights into comparative life histories.