This test was conducted to study the effects of cello-oligosaccharide and probiotics on intestinal barrier function of broilers in heat stress. Nine hundred 21-d-old Ross 308 broilers were randomly allocated to 5 groups: control (Con) group, heat stress (HS) group, probiotics (HS+PRO) group, cello-oligosaccharide (HS+COS) group and synbiotics (HS+SYN, SYN=PRO+COS) group. Birds were raised at 22 ℃ in Con group, and the others subjected to cyclic heat stress by exposing them to 33 ℃ from 08:00 to 18:00 and 22 ℃ from 18:00 to next day 08:00. Raising experiment period was 21 d. The results showed as follows: 1) compared with birds kept in Con group, average daily gain and average daily feed intake of birds in HS group was significantly reduced (P<0.05); the viable counts of Lactobacillus in cecal contents was significantly decreased (P<0.05), and the viable counts of Escherichia coli and Clostridium in cecal contents were significantly increased (P<0.05); jejunal villus height was significantly shorter (P<0.05), and the ratio of villus height to crypt depth was significantly lower (P<0.05); jejunal transepithelial electrical resistance (TER) value was significantly decreased (P<0.05), and the level of jejunal paracellular permeability of 4 kDa-FITC dextran (FD4) flux was significantly raised (P<0.05). 2) As compared with HS group, the average daily gain, average daily feed intake and feed to gain ratio of birds in HS+PRO and HS+COS groups were not significantly different (P>0.05); villus height and villus height to crypt depth ratio were significantly increased (P<0.05); flux of FD4 was significantly reduced (P<0.05). As compared with HS group, viable counts of Lactobacillus, Bifidobacterium, Escherichia coli and Clostridium in cecal contents in HS+PRO group were not significantly different (P>0.05), the viable counts of Lactobacillus in cecal contents was significantly increased (P<0.05), and Escherichia coli and Clostridium in cecal contents in HS+COS group were significantly decreased (P<0.05). 3) As compared with HS group, feed to gain ratio in HS+SYN group was significantly decreased by 4.21% (P<0.05); the viable counts of Lactobacillus and Bifidobacterium in cecal contents were significantly increased (P<0.05), and Escherichia coli and Clostridium in cecal contents were significantly decreased (P<0.05); villus height and villus height to crypt depth ratio were significantly increased (P<0.05); TER value was significantly increased (P<0.05) and the flux of FD4 was significantly reduced (P<0.05). These results indicate that additions of probiotics and cello-oligosaccharide are effective in partially ameliorating intestinal barrier function. The combination of probiotics and cello-oligosaccharid has better effect on ameliorating intestinal barrier function than supplementing them alone.