Metadiscourse, a linguistic means that is used in the production and organization of ideas, is vital in achieving successful communication. In language studies, metadiscourse in writing and speaking have been disparately investigated, where the former received more attention than the latter. Thus, the present study analyzes metadiscourse in the speech production of 57 Korean L2 learners purposively chosen relative to their language proficiency. The current results suggest two significant findings. First, the quantitative analysis of metadiscourse "frequency" reveals the interactional category's superiority over the interactive metadiscourse, which implies that the Korean L2 learners are more interested in interacting with the listeners than organizing discourse and asserting their role as speakers. Secondly, the quantitative and qualitative analyses suggest that the "logical connectives," "relational markers," "hedges," and "personal markers" are metadiscourse features that significantly predict Korean L2 speakers' speech proficiency. Except for "personal markers," these proficiency indicators reveal a clear-cut divergence regarding the levels of lexical sophistication and lexical expansion among the proficiency groups using a vocabulary profiler. The present study proves that speech proficiency in the Korean context depends on the employment of metadiscourse in frequency and diversity. Possible future applications and directions relevant to the present study are also provided.