The effects of dietary fiber isolated from ascidian (Halocynthia roretzi) tunic on the changes of weight, total gut transit time, serum cholesterol and glucose level were investigated in rats. Twenty four male rats were divided into 4 groups and were fed a control diet and three fiber supplemented diets with 5,10 and 20% of ascidian insoluble cellulose for 4 weeks, respectively. Food intake was not affected by the supplemented diet of ascidian cellulose but the body weight gain and food efficiency ratio were reduced in proportion to a feeding amount of ascidian cellulose. The fecal output and fecal water content were increased, gut transit time was shortened, and length of gut was elongated in all dietary fiber groups. Serum cholesterol, LDL-cholesterol, neutral lipid, phospho-lipid and serum glucose concentrations were lowered and HDL-cholesterol was increased in rats fed the ascidian insoluble cellulose diet in proportion to a feeding amount of ascidian cellulose.