This study aims to explore the concept and the range of discourse constructing competence and uncover the diverse aspects of Korean learners` use of grammar in terms of constructing discourse by specifically analyzing their writing. This study defines discourse constructing competence as competence in constructing the meaning of discourse according to the context and purpose of communication and organizing the discourse to perform a communicative function. Moreover, five constituents of discourse constructing competence were established: competence in generating meaning, competence in cohesion, competence in coherence, competence in rhetoric, and competence in considering context. As a result of analysis, aspects of using grammar were related to competence in cohesion, competence in coherence, competence in rhetoric, and competence in considering context. Furthermore, learners` discourse constructing competence is shown to have an influence on selecting and using grammar, and incomprehension about discourse led to erroneous uses of grammar. On the other hand, the use of proper grammar had the potential to improve the quality of discourse. Through this, a close correlation could be identified between discourse constructing competence and grammar use.