It is highly likely that Korean college students often commit inadvertant speech errors of replacing /t/ or /d/ with palatoalveolar /ʧ/ and /ʤ/ in the consonant clusters of /tr/ and /dr/. The writers presume that this is due to their confusion about the place of articulation of /t/ and /d/ with /ʧ/ and /ʤ/ /in /tr/ or /dr/ sequence, their lip-rounding difference from that of /ʧ/ and /ʤ/, and finally students’ inaccurate knowledge about the phonetic constraint of */ʧr/ and */ʤr/ in English syllable structure. Under such hypotheses this study analyzes the responses from an experiment group of fifteen Korean college students based on phonetic theories and probes into possible background reasons for this over-production as a form of speech errors.