This experiment was conducted to study the effects of probiotics (PRO) and cello-oligosaccharide (COS) on nutrient digestion, mRNA expression of intestinal mucosa amino acid transporters and nitrogen emission of broilers under heat stress. Nine hundred 21-day-old Ross 308 broilers were randomly allocated to 5 groups: thermoneutralzone (HN) group, heat stress (HS) group, probiotics (HS+0.15%PRO) group, cello-oligosaccharide (HS+0.15%COS) group and synbiotics (HS+SYN,SYN=0.15%PRO+0.15%COS) group. Birds were either raised in a thermoneutral zone (22℃) in HN group, and the others were subjected to cyclic heat stress by exposing to 33℃ from 08:00 to 18:00 and 22℃ from 18:00 to next day 08:00. Raising experiment period was 21 days. The results showed as follows: 1) compared with birds kept in HN group, average daily gain and average daily feed intake of broilers subjected to heat stress were significantly reduced 10.65% (P<0.05) and 8.04% (P<0.05), respectively. Average daily gain, average daily feed intake and feed to gain ratio of broilers subjected to heat stress with diet added probiotics or cello-oligosaccharide individually were not significantly different (P>0.05). Apparent digestibility of crude protein and crude fiber in HS group was significantly decreased (P<0.05), nitrogen intake and nitrogen retention were significantly decreased (P<0.05), nitrogen excretion and nitrogen excretion rate were significantly increased (P<0.05), ammonia nitrogen, uric acid contents in excreta and ammonia concentration in chicken house were significantly increased (P<0.05), the activity of urease in excreta was significantly increased (P<0.05), and mRNA expression of the basic amino acid transporter (rBAT), y⁺L amino acid transporter-2 (y⁺LAT2), cationic amino acid transporter-1 (CAT1) and cationic amino acid transporter-4 (CAT4) in intestinal mucosa was significantly down-regulated (P<0.05). 2) Compared with HS group, apparent digestibility of crude protein was significantly increased in HS+PRO and HS+COS groups (P<0.05), nitrogen excretion and nitrogen excretion rate in HS+PRO and HS+COS groups were significantly reduced (P<0.05), while nitrogen retention was significantly increased (P<0.05). Compared with HS group, excreta ammonia nitrogen content in HS+PRO group was significantly lowered (P<0.05), and ammonia concentration in chicken house and activity of urease in excreta of HS+COS group were significantly reduced (P<0.05). 3) As compared with HS group, apparent digestibility of crude protein and crude fiber were significantly increased (P<0.05) in HS+SYN group. Nitrogen excretion and nitrogen excretion rate in HS+SYN group were significantly reduced (P<0.05), while nitrogen retention was significantly increased (P<0.05). Ammonia nitrogen concentration in chicken house, excreta ammonia nitrogen content and urease activity of HS+SYN group were significantly reduced (P<0.05). and mRNA expression of rBAT in intestinal mucosa in HS+SYN group was significantly up-regulated (P<0.05). The results indicate that heat stress decrease nutrient digestion and increase nitrogen emission of broilers, and dietary addition of probiotics and cello-oligosaccharide are effective in partially ameliorating these changes. The combination of probiotics and cello-oligosaccharide is superior to individually addition.