The mechanism by which late bilinguals access the meaning of words presented in their second language (conceptual mediation or word association) is highly debated. Here we asked late Chinese-English bilinguals undergoing event-related potential (ERP) recordings to indicate whether pairs of English words were related or unrelated in meaning. Participants were unaware that half of the pairs concealed a repeated Chinese character when translated into Chinese. As expected, native English controls showed no sensitivity to this hidden factor. However, pairs of words unrelated in meaning and concealing form repetition through Chinese translation elicited longer reaction times, greater error rates, and larger N400 ERP shifts in Chinese participants. These findings demonstrate that Chinese participants unconsciously translate words into Chinese while reading English.