Effective communication strategies (CSs) has been shown to enhance L2 learners’ proficiency by a number of researchers. This study investigated Korean college EFL learners’ interactions to see what factors encourage the learners to use effective communication strategies in interpersonal communications. For this, the interpersonal interactions of six pairs, two high-high proficiency pairs (H-H), two high-low proficiency pairs (H-L), and two low-low proficiency pairs (L-L), were recorded twice and analyzed for the amount of token and CSs and choice of CSs. Interviews, observations, and personal backgrounds were also collected for this qualitative study. The results showed that interactional moves have more powerful influence on the use and choice of CSs rather than learners’ proficiency. The learner’s role in the interaction, the proficiency gap with the interlocutor, and collaborative relation appeared as strong factors that affect the amount of output and choice of effective strategies.