Within the input and interaction research paradigm, how learners' individual differences play a role in using learning opportunities during interaction has become one of the main areas of investigation. Recasts have also received much attention in interaction research. This paper explores the extent to which individual differences in grammatical sensitivity (GS) are associated with noticing of recasts and learning through task-based interaction. Twenty-two English-speaking learners of Korean at the beginning and intermediate university level participated in a series of communicative tasks in native speaker (NS)-non-native speaker (NNS) dyads. This experimental study employed a pretest, immediate-posttest and delayed-posttest design. The target structure was Korean object relative clauses; the NS in-terlocutor provided the NNS participant with recasts on relative clause errors during the treatments. Immediate retrospective verbal reports were administered during the treatments to qualitatively capture noticing. The learners' GS capacities were measured by the Modern Language Aptitude Test subtest, "Words in Sentences." The results suggest that GS may have a positive relationship to noticing of recasts and that GS and learning may be related. Specifically, regarding the relationship between GS and learning outcomes, learners with higher GS had a larger gain from the pretest to the delayed posttest than those with lower GS. (Contains 6 tables and 2 figures.)