The present study aims to investigate the identification of native vowel categories by adult individuals with Autism Spectrum Disorder (ASD) and estimate their reaction times in both normal and whisper registers; their responses were compared with those of typically developing individuals. The results demonstrated that there was no deficit for individuals with ASD in normal speech, but their responses in the whispered speech were impaired. Also, individuals with ASD responded quicker than controls in normal speech but slower in the whispered speech; still, their responses were quicker than the responses of the controls in the whispered mode. The findings can have implications for the understanding of auditory sensitivities and auditory processing time in individuals with ASD as well as for clinical practice.