The purpose of this study was to conduct an acoustic examination of the obstruent stops produced by Korean-English bilingual children in connection with the question of whether bilinguals establish distinct categories of speech sounds across languages. Stop productions were obtained from ninety children in two age ranges, five and ten years: thirty Korean-English bilinguals, thirty monolingual Koreans and thirty monolingual English speakers. Voice-Onset-Time (VOT) lag at word-initial stop and fundamental frequency (f[subscript 0]) in the following vowel (hereafter vowel-onset f[subscript 0]) were measured. The bilingual children showed different patterns of VOT in comparison to both English and Korean monolinguals, with longer VOT in their production of Korean stop consonants and shorter VOT for English. Moreover, the ten-year-old bilinguals distinguished all stop categories using both VOT and vowel-onset f[subscript 0], whereas the five-year-olds tended to make stop distinctions based on VOT but not vowel-onset f[subscript 0]. The results of this study suggest that bilingual children at around five years of age do not yet have fully separate stop systems, and that the systems continue to evolve during the developmental period.