Insects defoliating Bornean endemic dipterocarp seedlings at the Sepilok nursery were investigated. A total of 12 insect species were documented as new records. Two defoliators were adult beetles while 10 were larvae of moths and butterflies. The most frequently encountered insect species was Clethrogyna turbata Butler (Lepidoptera: Lymantriidae), which occurred on four dipterocarp species. Due to its high abundance, the larva caused severe defoliation to Shorea symingtonii, S. waltonii and S. kudatensis seedlings. Defoliation caused by other insects was minor. Some notes on the new records are provided in this paper. The importance and management of insects associated with the dipterocarp seedlings are also discussed.