The current study employed a neuro-imaging technique, Event-Related Potentials (ERP), to investigate real-time processing of sentences containing filler-gap dependencies by late-learning speakers of English as a second language (L2) with a Chinese native language background. An individual differences approach was also taken to examine the role of proficiency and working memory. Materials included a plausibility manipulation to look at whether a plausibility effect, the N400 effect, was found at the point of resolution, the verb, in filler-gap dependencies. The results suggest that, although the L2 speakers as a group are not sensitive to plausibility variations, correlational analysis indicates that more proficient L2 speakers, like the first-language (L1) speakers, are sensitive to plausibility variations while processing filler-gap sentences. Working memory was not found to be associated with more native-like processing of these constructions.