Backgrounds: Patients with functional constipation are often recommended to increase dietary fiber intake and overactive bladder (OAB) may be associated with bowel symptoms. We examined the associations among functional constipation, dietary fiber intake, and OAB in Korean population cohort. Methods: This cohort study, using a reliable and valid questionnaire based on the Rome III criteria was performed in Yangpyeong city, Korean community on subjects aged = 40 years between 2011 and 2012. Total, grain, vegetable, fruit and seaweed fiber intakes were estimated from dietary questionnaires. OAB was defined through overactive bladder symptom score. The associations among functional constipation, dietary fiber intake, and OAB were assessed separately by age and gender. Results: A total of 1,173 patients were enrolled, with mean age of 62.4±29.0, of which 63% was comprised of women. There were 134 (11.4%) patients with functional constipation. Total fiber intake was associated with a significantly lower prevalence of functional constipation in men, not in women. On the contrary, OAB was correlated with functional constipation in elderly women. Conclusion: Men who consumed high amount of fiber have a lower prevalence of functional constipation. OAB is associated with functional constipation in elderly women. This population-based study suggest that the pathogenesis of functional constipation may be different between men and women.