Ethnolinguistic minority students may have lower levels of metacognitive knowledge and English vocabulary knowledge than non-minority students. Nevertheless, few longitudinal studies have examined their growth trajectories of metacognitive knowledge and English vocabulary knowledge over time. Drawing upon a latent growth curve model, the present study aims to contrast two groups of students' growth trajectories in metacognitive knowledge and breadth of English vocabulary knowledge: with a sample of 115 ethnolinguistic "Yao" minority and 108 ethnolinguistic majority "Han" students. The results showed that both groups improved their metacognitive knowledge and breadth of English vocabulary knowledge from third grade to sixth grade in a cumulative trend. Metacognitive knowledge predicted the breadth of English vocabulary knowledge throughout the examined school years. The results also highlighted differences in the students' development of metacognitive knowledge and breadth of English vocabulary knowledge. The ethnolinguistic "Yao" minority students lagged behind their ethnolinguistic majority "Han" counterparts. The findings suggest a need for pedagogical interventions to enhance ethnolinguistic minority students' metacognitive knowledge and English vocabulary knowledge.