We investigated the efficacy and safety of a new type of dietary fiber (high specific volume polysaccharide) for use in treating constipation of different etiologies. Functional constipation patients and irritable bowel syndrome-constipation (IBS-C) patients were administrated high specific volume polysaccharide (HSVP) three times daily for a period of 2 wk to relieve their symptoms. Scores on a stool form scale, and patient reports of straining during a bowel movement, having sensations of an incomplete bowel movement or a blocked anorectum, and abnormal defecation intervals were recorded, graded, and scored by a functional constipation sample group. Similarly, a cohort of IBS-C patients reported their occurrence of abdominal discomfort or pain, abnormal stool formation, defecation frequency, and straining during a bowel movement. Additionally, both groups reported any adverse reactions associated with taking HSVP. All patients in both groups returned for follow-up visits, and no adverse reactions to treatment with HSVP were reported. In the functional constipation group, HSVP was effective for treating symptoms of constipation in 81.46% and 93.17% of patients after 7 and 14 d of dosing, respectively (both p<0.05). In the IBS-C group, symptoms of constipation were relieved in 71.67% and 88.34% of patients after 7 and 14 d of dosing, respectively (both p<0.05). High specific volume polysaccharide was shown be effective for treatment of functional constipation and IBS-C, without causing significant adverse events.