The present work examines the impact of code-switching (CS) on novel word learning in adult second language (L2) learners of Spanish. Participants completed two sessions (1-3 days apart). In the first session, they were taught 32 nonwords corresponding to novel creatures. Training occurred across 4 conditions: (1) a sentence in English only, (2) a sentence in Spanish only (the L2), (3) a sentence that contained CS from Spanish-to-English, (4) a sentence that contained CS from English-to-Spanish. Immediately after training, participants were tested on their ability to identify the newly trained words using a looking-while-listening paradigm in which videos of participants' looking patterns were collected remotely via Zoom. In the second session, re-testing of the trained words was completed. In the first session, training in the English-only condition led to better initial learning compared to the other conditions. In the second session, the English-only condition still had the highest accuracy, but performance in the two CS conditions was significantly better compared to the Spanish-only condition. These findings suggest that CS during vocabulary training may aid the retention of newly acquired word-object relations in the L2, compared to when training occurs entirely in the L2. This work has important implications for theories of L2 acquisition and can inform instruction practices in L2 classrooms.