The aim was to examine the expression of tight junction proteins, namely claudins 1 and 5 (CLD1 and 5) and the effects of probiotics-feeding on their expression in the gastrointestinal tract. In experiment 1, the expression of CLD1 and 5 was examined in chicks fed with starter rations for 7 days post-hatching. At day 7 the proventriculus, ileum, cecum and colon were collected for RT-PCR analysis of CLD1 and 5 gene expression. In experiment 2, the chicks were arranged in 3 groups: control group, probiotics group I and probiotics group II, which were fed with starter rations containing 0, 0.2 or 0.4% probiotics, respectively, for 14 days. The proventriculus, ileum, cecum and colon were collected in all groups at D0, D7 and D14 for analysis of CLD1 and 5 expressions by real time PCR. The expressions of CLD1 and 5 were detectable in all segments. Probiotics-feeding did not affect the expression of the CLD1 at D7 and D14 in the proventriculus, ileum and cecum. However, in the colon the expression of CLD1 was higher in probiotic group I than control and probiotics group II. The expression of CLD5 did not show significant differences except in the colon at D7 where control group was higher than that of D0 and D14 and higher in probiotic group I than probiotics group II. These results suggest that probiotics-feeding may not have effects on the gene expressions of CLD1 and 5 in the proventriculus, ileum and cecum. In contrast, probiotics-feeding may enhance the expression of CLD1 in the colon of broiler chicks. This result suggest that probiotics-feeding enhanced the expression of CLD1 in the colon and may help in maintaining tight junction functions and reducing the risk by pathogenic invasions.