The efficient use of working memory (WM) increases the potential of a learner’s cognitive abilities in learning through multimedia. The present study aims to explore the role of working memory in vocabulary learning through multimedia input. In particular, we explore the possible associations between two components of WM – executive WM and phonological short-term memory (PSTM) – and the effects of three types of input conditions (Definition + Word information + Video, Definition + Word information, and Definition) on second language (L2) vocabulary learning. A total of 95 students completed learning under the three conditions and took two WM tests: a reading span test, which measures complex executive WM, and a non-word span test, which gauges PSTM. We administered a vocabulary knowledge test, which included receptive and productive vocabulary knowledge, immediately and after two weeks. Our findings, based on repeated-measures analysis of covariance (ANCOVA), support the pronounced effects of the Definition + Word information + Video condition in vocabulary learning and retention, as well as the significant role of complex and phonological WM in vocabulary learning and retention under the three conditions. Theoretical and pedagogical implications concerning the role of WM in vocabulary learning through multimedia input are discussed.