This study aims to investigate the relationship between phonological alternation and morpheme-internal phonotactics. Drawing from discussions in recent literature regarding the matches and mismatches between phonological alternation and phonotactics, the study explores the influence of phonotactics on phonological alternation in two ways. First, phonotactic constraints are extracted from the Korean monomorphemic lexicon via the ‘Maximum Entropy Phonotactic Learning Model.’ Using the resulting grammar, I evaluate the well-formedness of forms subjected to phonological alternations compared to those unaffected. Results indicate a significant relationship between phonotactic constraints and phonological alternations. Specifically, obstruent nasalization and obstruent tensification are reinforced by robust morpheme-internal phonotactics, while phenomena such as t-palatalization, lateral nasalization, lateralization, and glide formation appear to be inhibited by weaker morpheme-internal phonotactics. Furthermore, focusing on nasalization, lateralization and glide formation, for which frequency data is available, this study statistically tests and assesses if the well-formedness of applied and unapplied forms influence the realization rate of phonological alternations. Secondly, I explore how the morpheme-internal phonotactic constraints interact with other constraints, such as faithfulness constraints, during the realization of phonological alternations at morpheme boundaries. The analysis reveals that certain morpheme-internal phonotactic constraints are weighted and, thus interact with other constraints, influencing the realization of phonological alternations. Nevertheless, the realization rate of glide formation is not fully captured by the ill-formedness scores assigned by the phonotactic constraints, highlighting the necessity for constraints reflecting morpheme information. In summary, this research illuminates the relationship between Korean phonological alternations and phonotactic constraints.