Abstract: Mismatch Negativity (MMN) generally increased as a function of the degree of discrepancy from the standard-stimulus duration. The MMN generator is indeed sensitive to even very small amounts of stimulus energy. The main objective of this study was to investigate the cortical activation of level-to-contour tone changes in different vowel duration indexed by mismatch negativity. Twenty-two healthy right-handed adults participated in this study. It was found that the long-to-short vowel duration changes with level-to-falling/rising and falling/rising-to-level tone changes perception elicited MMN between 196-220 msec with reference to the standard-stimulus Event-related Potentials (ERPs). The long-to-short vowel duration and level-to-falling/rising tone changes elicited a strong MMN bilaterally for both native and nonnative speakers of Thai, unlike short-to-long vowel duration and falling/rising-to-level tone changes. Source localization analyses performed using Low Resolution Electromagnetic Tomography (LORETA) demonstrated that sources were obtained in the Middle Temporal Gyrus (MTG) of the left hemisphere and in the Superior Temporal Gyrus (STG) of the right hemisphere for both subject groups.