This study investigated the impact of language sample length on mean length of utterance (MLU) and aimed to determine the minimum number of utterances required for a reliable MLU. Conversations were collected from Mandarin-speaking, hard-of-hearing and typical-hearing children aged 16-81 months. The MLUs were calculated using sample sizes ranging from 25 to 200 utterances. The results showed that for an MLU between 1.0 and 2.5, 25 and 50 utterances were sufficient for reliable MLU calculations for hard-of-hearing and typical-hearing children, respectively. For an MLU between 2.5 and 3.75, 125 utterances were required for both groups. For an MLU greater than 3.75, 150 and 125 utterances were required for hard-of-hearing and typical-hearing children, respectively. These findings suggest that a greater number of utterances are required for a reliable MLU as language complexity increases. Professionals working with hard-of-hearing children should consider collecting different numbers of utterances based on the children's language complexity levels.