OBJECTIVE: To evaluate the proper ingested volume of dietary fiber for relieving constipation in children. STUDY DESIGN: During a 3-year period, we prospectively evaluated the correlation of intake volume of dietary fiber with improvement of constipation in children. Patients were categorized into younger (3-7 years) and older (8-14 years) children. The evaluation period lasted 12 weeks. A good improvement was defined as the child exhibiting at least 60% relief of the constipation symptoms during the observation period. Freedom from constipation was observed during the last 4 weeks. RESULTS: The study population consisted of 422 patients (213 younger, 209 older), with a mean age of 7.89 +/- 4.71 years. Baseline daily dietary fiber intake of the younger and older groups was 5.97 +/- 2.35 g and 9.83 +/- 3.51 g, respectively. 227 cases (53.8 %) showed improvement of constipation, and 49.1 % of the patients had relief of constipation. Greater intake of dietary fiber was positively associated with good improvement of constipation in both groups (P = .002, and P < .001). Cutoff volumes of daily dietary fiber intake in the relief of constipation were 10 g in the younger group and 14.5 g in the older group. CONCLUSION: The cutoff of dietary fiber intake needed to relieve constipation increased with age, achievable in a 12-week intervention.