In this study, we investigated laxative effects of Sargassum fulvellum (S. fulvellum, SF) on loperamide-induced constipation in mice. First, the hot water extracts of SF (SFH) showed higher carbohydrate contents (26.65 ± 0.53%) than protein (9.41 ± 0.31%) and phenol (2.82 ± 0.00%). Oral administration of SFH effectively increased the body weight and the food intake decreased by loperamide intake in mice. Also, SFH improved the intestinal function by significantly increasing the number, weight and moisture contents of fecal pellets in loperamide-treated mice. Taken together, these results indicated that SFH has laxative effects on loperamide-induced constipation in mice and it might be used as a natural food material for improving or preventing constipation.