Previous studies have indicated that bilingualism may facilitate lexical learning in adults. The goals of this research were (i) to examine whether bilingual influences on word learning diverge for phonologically-familiar and phonologically-unfamiliar novel words, and (ii) to examine whether increased phonological memory capacity can account for bilingual effects on word learning. In Experiment 1, participants learned phonologically-familiar novel words that were constructed using the phonemes of English--the native language for all participants. In Experiment 2, participants learned phonologically-unfamiliar novel words that included non-English phonemes. In each experiment, bilingual adults were contrasted with two groups of monolingual adults: a high memory-span monolingual group (that matched bilinguals on phonological memory performance) and a low-span monolingual group. Results showed that bilingual participants in both experiments outperformed monolingual participants, both high-span and low-span. High-span monolinguals outperformed low-span monolinguals when learning phonologically-unfamiliar novel words, but not when learning phonologically-familiar novel words. The findings suggest that the bilingual advantage for novel word learning is not contingent on the phonological properties of novel words, and that phonological memory capacity as measured here cannot account for the bilingual effects on learning.