Irritable bowel syndrome (IBS) is a common functional disorder of the gastrointestinal system, and is characterized by abdominal pain, diarrhea (IBS/D), constipation (IBS/C), and alternating diarrhea and constipation (IBSC/A). The purpose of this study was to examine the impact of a four week kiwifruit intervention on bowel function in patients diagnosed with IBS/C. Fifty-four patients with IBS/C and 16 healthy adults participated in this study. All subjects participated in the 6 week, three phase study, which included a baseline phase (1 week), a dietary intervention period (4 weeks), and a post-intervention phase (1 week). Forty-one IBS/C patients and all healthy adults consumed two Hayward green (Actinida deliciosa var) kiwifruits per day for 4 weeks. Thirteen IBS/C patients in the control group took two placebo capsules per day for 4 weeks. Colon transit time was measured immediately prior to and following the intervention period. All subjects completed daily defecation records. After the 4-week intervention, weekly defecation frequency significantly increased in the IBS/C group of participants who consumed kiwifruit (p<0.05). Colon transit time significantly decreased (p=0.026) in the IBS/C group that consumed kiwi fruit. These findings suggest that kiwifruit consumption for 4 weeks shortens colon transit time, increases defecation frequency, and improves bowel function in adults diagnosed with IBS/C.