Background and Objectives: This prospective, randomized, controlled study aimed to evaluate the effects of flaxseed supplementation on functional constipation and quality of life in adult men and women in China. Methods and Study Design: 90 subjects with functional constipation diagnosed by the Rome IV criteria were enrolled. Subjects were randomly assigned to receive either 50 g/day flaxseed flour with meals (n=60) or 15 mL/day of a lactulose solution on an empty stomach (n=30) every morning for 4 weeks. Wexner constipation scores, stool consistency according to the Bristol Stool Form Scale, and bowel habits (frequency of bowel movements/week, the time spent on defecation) were the primary outcomes. The change in Patient Assessment of Constipation Quality of Life score was the secondary outcome. Results: After 4 weeks, the bowel habits in both groups were significantly improved. The median Wexner constipation score decreased from 14 to 6.5 in the flaxseed group (p＜0.001) and from 15 to 9 in the lactulose group (p＜0.001). The median defecation frequency per week increased significantly (2 to 7 for flaxseed and 2 to 6 for lactulose, p＜0.001 for both groups). The Patient Assessment of Constipation Quality of Life score decreased significantly (-1.34 and -0.66 for flaxseed and lactulose, respectively; p＜0.001 for both groups). Conclusions: Flaxseed flour is somewhat more effective at increasing defecation frequency than lactulose, improving bowel movements and promoting life quality of subjects with chronic functional constipation in the Chinese population.