The aims of the study are to demonstrate the effect of probiotic use on the healing of radiation proctitis (RP) and evaluate the efficiency of fecal biomarkers at follow-up of the treatment. Thirty-two male/female rats were randomly separated into four groups of eight rats. The first group (control) was not radiated. RP was created by 17.5 Gy single dose rectal irradiation. The second group (RP) was subjected to RP, but not treated. The third group (RP+ASA) was treated with 5-aminosalicylic acid (5-ASA) 250 mg/kg daily by gastric lavage for 14 days after the irradiation, and the forth group (RP+LGG) was treated with Lactobacillus GG (LGG) 25x100 million CFU daily. Feces samples were taken at the 7th and 14th day of the treatment for fecal biomarkers. Rectums of the rats were resected at the 14th day by laparotomy. Samples were evaluated both macroscopically and microscopically. RP was achieved both macroscopically and microscopically. Weight loss of RP group is statistically significant (p<0.005) than other groups. The healing ratio of RP+ASA and RP+LGG groups was significantly better than the RP group (p<0.005) both macroscopically and microscopically. But there was no significant difference between ASA and LGG groups. Biochemically, fecal calprotectin was found to be more effective than fecal myeloperoxidase and fecal lactoferrin to show the efficacy of treatment of radiation proctitis. The results of our study demonstrate that probiotic is as effective as 5-aminosalicylic in the treatment of radiation proctitis, and fecal calprotectin is a useful biomarker in determining the response to the treatment.