This study was conducted to determine if dietary fiber would reduce exposure of the tissues to dietary benzo[a]pyrene(BP) , a well-known carcinogenic polycyclic aromatic hydrocarbon, as evaluated by benzo[a]pyrene hydroxylase (BPH) activity. The effects of three different sources of dietary fiber(pectin, polydextrose, and clellulose) on BPH activity were studied using Sprague-Dawley rats. In this study, male rats were fed a fiber-free purified diet for 7 days, whereupon they were switched to experimentla diets for 48h. After 48h, their liver, stomach , small intestinal mucosa and large intestinal mucosa were assayed for BPH activity. Thissues exposed to benzo[a]pyrene(400mg/kg diet, fiber-free) showed significant increse in the activity of BPH ; 27 times in liver, 7 times in stomach, 18 times in small intestinal mucosa and 3 times in large intestine. The inhibition in BP -induced BPH activity by dietary fiber in liver, stomach and small intestinal mucosa was observed in the decreasing order : 10 % perctin > 10% polydextrose >5 % polydextrose > 10% cellulose. Decreased BPH induction indicates that soluble dietry fibers, especially pectin and polydextrose in this study, protect the tissues of digestive system from exposure to BP.