【Objective】 To identify the mean length of the three longest utterances(MLU3)development in Mandarin-speaking toddlers aged 16 to 30 months. 【Methods】 Using face-to-face interviews with the CCDI(Chinese Communicative Development Inventory-Mandarin Version),parents of 194 toddlers aged 16 to 30 months randomly selected in two urban districts in Shenyang were asked to report three of their children's longest utterances.Then calculated the MLU3 of each child.Next it was given that childrens' MLU3 change with age. 【Results】 184 toddlers entered the study.The MLU3 value increased with the age increase gradually.Linear regression analysis showed that MLU3 was positively correlated with age(r=0.742);The MLU3 of 23 months group was more than that of 22 months group,the difference was statistically significant(P<0.01);The MLU3 of rest adiacent groups showed no significant difference. 【Conclusions】 The mean length of the three longest utterances in Mandarin-speaking toddlers developes gradually as age increased from 16 months to 30 months.22~23 months is the rapidly period for MLU3 development.