This study researched the feature of university students` voice realization of the combinations structure of noun stem-final consonant followed by vowel postposition, and explained the cause of such practice by lexical usage frequency and phonological strength in Korean language based on the result The result of this study can be summarized as follows; Firstly, in case of ‘milk(jot) and caldron(sot) in low frequency noun, /ㅅ/ alternation realization ratio appeared as high. This is interpreted as low frequency vocabulary experiences restructuring, according to the frequency effect theory of vocabularies. Secondly, in case of the combination of ‘flower(kkot)’ and ’light(bit) as high frequency noun + vowel postposition, standard pronunciation ratio is high. As the frequency of use is high for these vocabularies, the vocabulary pattern is strengthened and alteration type erroneous pronunciation can only be low. Thirdly, the reason why the non ending with /ㅌ/ pronunciation has higher realization ratio of [ㅊ] than [ㅅ], is found as for adjusting relative phonological strength in the syllable structure, and according to the syllable head law.