169 Background: Concurrent chemoradiotherapy(CCRT) has become a promising treatment for esophageal cancer. Mostly, however, 3 week or 4 week interval of conventional FP(5-fluorouracil plus cisplatin) regimen is adopted, which is usually associated with moderate to severe treatment-related toxicities. Studies about weekly regimen of FP CCRT are little known, thus we studied the efficaty, tolerability and toxicities of weekly FP CCRT regimen. Methods: From February 2010 to august 2015, Patients staging from I to III esophageal cancer(according to AJCC 7th edition) were enrolled, who were received radiation therapy with dose of from 50.4Gy to 60Gy(5 days/week) and 5-FU 1000mg/BSA with cisplatin 30mg/BSA weekly. Results: From February 2010 to august 2015, 50 patients: male/female 47/3, median age 71.5 (47-78), all of 50 patients was squamous carcinoma, well/moderately differentiated carcinoma 1/18. 45 patients completed CRT without dose reduction, 9 patients received less than 6 cycles of chemotherapy, 4 patients received less than 50.4Gy of radiotherapy. Major toxicities of grade 3 or less were as follows: neutropenia 52%, thrombocytopenia 21%, nausea & vomiting 10%, fatigue 10%, anemia 5%. Toxicities over grade 4 was seen only in 1 patient. 15 patients showed complete response. The median overall survival was 10.67 months(4-48). The median disease-free survival was 16.9 months. Conclusions: Weekly regimen of concurrent CRT with 5-FU and cisplatin resulted in less toxicities over grade 3. Although, this regimen still showed non-inferiority to previous conventional 4 week-interval FP CCRT regimens in terms of PFS and OS. In this study, 82% of our patients had completed CCRT without any interruption. Hence, our results suggest that CRT with weekly 5-FU and cisplatin as definitive treatment for esophageal cancer could be a tolerable regimen.