BACKGROUND : This study aimed to objectively investigate whether the addition of polydextrose to sterilized probiotic containing Lactobacillus helveticus will confer benefits to constipation-predominant irritable bowel syndrome patients. METHODS : A total of 163 patients were randomized into two groups: Group A to consume 350 mL of sterilized probiotic with 5.85 g polydextrose daily for 1 week and Group B without polydextrose. Intestinal transit time, fecal pH, fecal weight, and modified Garrigues questionnaires for pre- and post-consumption were assessed. RESULTS : Median intestinal transit time was significantly reduced from 58 (IQR 43-72) to 45 (IQR 24-59) hours and 48 (IQR 31-72) to 30 (IQR 24-49) hours for Groups A and B, respectively (p < 0.01). Fecal pH for Groups A and B was significantly reduced from 6.57 ± 0.96 to 6.13 ± 0.95 (p = 0.003) and 6.58 ± 1.0 to 5.87 ± 0.83 (p < 0.001), respectively. Fecal weight for Group A was significantly increased from 8 g ± 6.4 g to 9.8 g ± 7.6 g (p = 0.003), but it was reduced for Group B from 13.3 g ± 19.4 g to 11.2 g ± 6.6 g (p = 0.308). Constipation-related symptoms were significantly improved for both groups. CONCLUSIONS : The addition of polydextrose to sterilized probiotic containing L. helveticus did not show significant benefits to constipation-predominant irritable bowel syndrome patients. However, daily consumption of sterilized probiotic containing L. helveticus with or without polydextrose for a week alleviated constipation-related symptoms and objectively reduced both fecal pH and intestinal transit time.