Objective:To investigate the age of onset of functional constipation in children and to explore its relationship with possible factors.Methods:Four hundred and sixteen children with functional constipation who were admitted to the Digestive Specialist Clinic of Nanjing Children′s Hospital from January 2017 to December 2018 were divided into 4 groups (Q1-Q4) according to the quartiles of the onset age.The gender, duration of symptoms and constipation of their parents of the 4 groups were analyzed.Results:Age of onset of 416 children was (1.58±1.64) years, the age of onset in the Q1 group was (0.27±0.19) years, the age of onset in the Q2 group was (0.82±0.17) years, the age of onset in the Q3 group was (1.64±0.32) years, and the age of onset in the Q4 group was (3.91±1.83) years.The constipation duration in 416 patients was (1.50±1.62) years; the constipation duration of Q1, Q2 and Q4 groups was (2.20±1.95) years, (1.33±1.48) years, (1.11±1.05) years and (1.35±1.66) years, respectively, and the group with the youngest age of onset (Q1) had the longest duration of constipation, which was statistically significant compared with the other three groups ( F=9.644, P<0.05). Of the 416 children, 190 cases (45.7%) were boys, 226 cases (54.3%) were girls; 54 boys (50.9%) and 52 girls (49.1%) in the Q1 group, 47 boys (39.8%) and 71 girls (60.2%) in the Q2 group, 39 boys (40.6%) and 57 girls (59.4%) in the Q3 group; 53 boys (55.2%) and 43 girls (44.8%) in the Q4 group; there were no significant differences in gender ( χ2=7.210, P>0.05). Among 416 children with FC, 196 cases (47.1%) had at least one of their parents with constipation symptoms, including 61 cases (57.5%) in Q1 group, and 66 cases (55.9%) in Q2 group, 34 cases(35.4%) in Q3 group, 35 cases (36.5%) in Q4 group.The 2 groups (Q1-Q2) with younger onset compared with the older onset children (Q3-Q4), their parents were more likely to have constipation symptoms, and the difference was statistically significant ( χ2=17.96, P<0.05). Conclusions:The age of onset of functional constipation in children is young, and younger functional constipation children are less likely to receive formal guidance treatment at an early stage; gender has no significant relationship with the age of onset; children with a younger onset, genetic factors are more meaningful to them.