Influences of galactosylsucrose and xylosylfructoside on body mass gain, the digestive tract mass and concentrations of organic acids such as acetic, propionic, butyric, lactic and succinic acid in the cecum were compared among rats fed a cholesterol-enriched fiber-free diet [cholesterol 6 + cholic acid 1.5 (g/kg)] containing either galactosylsucrose, xylosylfructoside or sucrose (100 g/kg) or the above fiber-free diet without test sugar (control) for 21 d. Body mass gain was greater in rats fed sucrose, but not in rats fed galactosylsucrose or xylosylfructoside, than in control rats. The mass of the small intestine and colon plus rectum was larger in rats fed xylosylfructoside than in control rats. Cecal contents and cecal tissue mass were heavier, water content of cecal contents was higher, and pH and ammonia concentration of cecal contents were lower in rats fed diets containing xylosylfructoside than in control rats. Galactosylsucrose had similar effects, although not all differences were significant. The concentration of hydrogen ion in cecal contents positively correlated to total cecal concentration of measured organic acids and to amount of cecal contents. Total concentration of measured organic acids in cecal contents positively correlated to cecal tissue mass. The estimated contribution of galactosylsucrose, xylosylfructoside and sucrose for body mass deposition were 0.19, -0.29 and 0.51 (g body mass gained/g sugar), respectively.