This study was performed to investigate the sound distortion following the alternation of the palatal plate thickness, for this study, 3 subjects who were born in Seoul and spoke Seoul dialect were recruited from K university male student population. First, their sounds of /아(a)/, 어(e)/, 오(o)/, 우(u)/, 으($.{+}$), 이(i)/,에(e)/ without inserting plate were recorded , and then the sounds with palatal plates of different thickness were recorded, respectively. The palatal plates was constructed to cover the alveolar & palatal surfaces of the maxilla with an approximate thickness of 1.0mm, 2.5mm, and thickness of 2.5mm over the alveolar ridge & 1.0mm elsewhere and, named B, C, D-type, in succession. Series of analysis were administered through Computer (16 bit IBM PC/AT) at analyze the sound distortions. These experiments were analyzed by the LPC, Log Area Ratio. The findings led to the following conclusions: 1. Sound distortions were relatively minute in each condition and informations, however, /이(i)/ was the most distorted vowel in all conditions. 2. By and large, sound distortion was large in C, D-types. However, there was no correlation of the distortion rate on the 3 informants, and all tested vowels. 3. It was similar to LPC, Log Area Ratio distortion rates. 4. It was found that the sound distortion wit]1 plate inserted was verified to the numeric value with LPC and Log Area Ratio method.