This study examines EFL (English as a foreign Language) teachers' technological pedagogical content knowledge (TPACK) and how such knowledge affects the adoption of mobile-assisted language learning (MALL). A total of 158 in-service Taiwanese English teachers were surveyed. Two frameworks were employed to examine latent constructs: TPACK and the technology acceptance model (TAM). Descriptive statistics showed that among TPACK variables, technological pedagogical knowledge possessed the highest mean score. In terms of TAM, EFL teachers scored continuous usage (CU) highest, therefore implying that they were keen to use MALL in their lessons. The partial least square approach was applied to identify structural relationships between the proposed variables; it revealed that TPACK significantly affected both perceived ease of use (PEU) and perceived usefulness (PU). Furthermore, PEU significantly affected PU, which was shown to have a significant effect on both attitude toward use (ATU) and CU. The mediation effects of PU on the relationship between PEU and ATU, as well as CU, were also confirmed. Hence, TPACK was critical to MALL's adoption, and its PU was pivotal to teachers' attitudes toward and continued use of it.