This study explored the differences in mean length of utterance (MLU) and mean length of the five longest utterances (MLU5) between 5-6-year-old Mandarin-speaking children, and between typically developing children and children with developmental language disorders (DLD). Eighty-nine typically developing children and 35 children with a DLD participated in this study. The researchers collected, transcribed, and analysed language samples from these children. MLU and MLU5 were analysed and compared between the groups. The results showed that MLU and MLU5 were significantly higher for 6-year-olds than 5-year-olds. Also, both MLU measures were significantly lower for children with DLD than for typically developing children. The findings demonstrate that MLU and MLU5 can be used to evaluate language ability and to identify children with DLD among Mandarin-speaking children aged 5 and 6 years.