<p>This cross-sectional study investigated associations between classroom English competency and teaching efficacy among English Medium Instruction (EMI) lecturers in Vietnamese higher education. Data were collected from 187 Vietnamese national lecturers across 12 public universities using the Classroom English Competency Scale and Teaching Efficacy Scale. Results revealed a strong positive association between classroom English competency and teaching efficacy (r = .68, p &lt; .001), with instructional language skills emerging as the strongest predictor (β = .38, p &lt; .001). Hierarchical regression analysis indicated that classroom English competency components explained 47.2% of variance in teaching efficacy beyond control variables. Pedagogically-oriented competencies (instructional and interactive language skills) demonstrated substantially stronger associations than general language competencies (grammar, vocabulary, pronunciation). The cross-sectional design establishes associations but cannot determine causal direction; findings should be interpreted as relationships rather than causal effects. Vietnam’s distinctive EMI context—rapid policy-driven expansion without corresponding infrastructure—shapes interpretation and suggests cautious generalization to settings with different implementation trajectories or institutional support. The study contributes component-level evidence for Freeman’s English-for-Teaching construct while informing professional development programs targeting pedagogical language competencies in policy-driven EMI expansion contexts. Longitudinal research is needed to establish temporal precedence and examine causal pathways between language competency development and teaching efficacy.</p>