Purpose: This study examined the effect of phonological overlap on English and Spanish expressive vocabulary accuracy as measured by the bilingual Expressive One-Word Picture Vocabulary Test--Fourth Edition (EOWPVT-IV). We hypothesized that if languages interact during an expressive vocabulary task, then higher phonological overlap will predict higher expressive vocabulary accuracy, especially in the nondominant language. Method: Twenty English-dominant bilingual children (English-Spanish) completed the bilingual EOWPVT-IV. We calculated phonological overlap between 117 English and Spanish words included in the bilingual EOWPVT using the Crosslinguistic Overlap Scale for Phonology. Results: Generalized logistic mixed-effect models revealed that phonological overlap and word frequency predicted vocabulary accuracy in Spanish, in addition to item difficulty. Age and item difficulty were the only predictors of English accuracy. Conclusions: Phonological overlap was a significant predictor of Spanish vocabulary accuracy (the least dominant language of the children in our sample), suggesting a transfer between vocabulary in the dominant language into vocabulary in the least dominant language. Future studies should investigate how languages interact in bilingual children to provide us with information about how to create and administer vocabulary tests that represent vocabulary in each language and use vocabulary teaching strategies that promote dual language development.