The physicochemical and in vitro physiological properties of soluble dietary fiber (SDF) from wax gourd (Benincasa hispida) pulp and peel were investigated. The pulp was composed of 11.4% SDF and 24.3% insoluble dietary fiber (IDF), while the peel contained 3.2% SDF and 43.3% IDE The predominant sugar in the SDF of the wax gourd pulp and peel was uronic acid, followed by galactose and rhamnose. The SDFs from the wax gourd pulp and peel gave similar elution patterns, with 4 main neutral sugar and uronic acid peaks eluted by 0.4, 0.5, 1, and 2 M ammonium acetate buffer. The pulp SDF had a much higher glucose retardation index (GRI) than the peel SDF for all measurement times. The pulp SDF showed strong growth-inhibiting activity against Escherichia coli and Clostridium perfringens, whereas the peel SDF produced strong growth-promoting activity against Bifidobacterium longum, Bifidobacterium infantis, and Lactobacillus brevis when compared to glucose.