This study investigated the effect of word class on the acquisition of L2 ambiguous words using electroencephalogram (EEG) technology. We asked Chinese (L1)-English (L2) bilinguals to learn a set of English pseudowords paired with one or two semantically unrelated Chinese meanings, including pseudowords paired with an unambiguous noun meaning (N-unA), pseudowords paired with two noun meanings (NN), and pseudowords paired with a noun meaning and a verb meaning (NV). We recorded three ERP components during learning: P200, N400, and LPC. Behavioral results showed that it was easier to learn ambiguous words with two noun meanings than those with one noun and one verb meaning; unambiguous words were learned better than ambiguous words. The ERP results showed that NV elicited larger P200 and LPC than NN, whereas NN elicited larger N400 than NV, suggesting that the word class of different meanings impacts L2 ambiguous word acquisition, and this word class effect can occur at the initial memory encoding stage of learning. Overall, our results revealed the specific effect of word class on the acquisition of L2 ambiguous words.