This study aimed to make a comparison of the non-word repetition performances be-tween inner and overt speech of the adults with and without stuttering (AWS and AWOS). The 29 pairs of AWS and AWOS were recruited by matching their ages, genders and edu-cation levels. All of the participants were assessed by the Revised Stuttering Severity In-strument-4 for Mandarin-Speaking Adults to determine whether they had stuttering or not. Then, both of the groups repeated the non-words in two speech conditions, inner and overt, separately. The three measures including response time (RT), accuracy ratio (AR) and dis-fluency ratio (DR) in the task of non-word repetition were recorded and t-tests and two-way mixed ANOVA were employed to examine whether the differences existed in the three measures between the two groups and between the two speech conditions. The results of this study showed that for both the inner and overt speech, the performances on the three measures (RT, AR and DR) in NWR of the AWS were significantly poorer than those of AWOS. Ad-ditionally, for both the groups, the DRs in NWR in the inner speech were significantly higher than those in the overt speech, but no significant difference existed in AR of NWR between the inner and overt speech. The results showed that AWS may have phonological processing difficulties so that they took more time and made more mistakes than AWOS. Also, the dis-fluencies of AWS might occur in inner speech before they spoke out bumpily.