This intervention study examined the effect of English morphological instruction on the development of English as well as Malay morphological awareness and word reading abilities among Malay-English bilingual fourth graders in Singapore, where English is the medium of instruction. The intervention group experienced semester-long instruction in English derivation; the control group was taught with their regular English curriculum. Both groups were tested with derivational awareness and derived word decoding tasks in English and Malay at the end of Grade 3 prior to the intervention (pre-test) and at the end of the first semester of Grade 4 right after the intervention (post-test). There was no significant difference between the two groups on all tasks at pre-testing. Significant intervention effects were found on the development of English abilities in that the intervention group's performance gain was significantly greater than that of the control group on all English tasks except the derived decoding fluency task. More important, such intervention effects were also evident with some Malay tasks. These findings provide empirical evidence that supports the benefits of morphological instruction to bilingual children's reading development and a possibly causal effect of cross-linguistic transfer of morphological awareness from English to Malay.