Background: Efficacy of chemotherapy plus bevacizumab has been shown in patients with metastatic colorectal cancer (mCRC) compared with chemotherapy alone. The aim of the present study was to evaluate the efficacy and safety of FOLFIRI or XELIRI regimens in combination with bevacizumab for mCRC patients in a first-line setting. Materials and Methods: A total of 132 patients with previously untreated and histologically confirmed mCRC were included. They were treated with either FOLFIRI-Bevacizumab (Bev) or XELIRI-Bev according to physician preference. The efficacy and safety of the two regimens were compared. Results: Between 2006 and 2010, 68 patients were treated with the XELIRI-Bev regimen, while the remaining 64 patients received the FOLFIRI-Bev regimen. The median age was 58.5 years (53.6 years in the FOLFIRI-Bev and 59.7 years in the XELIRI-Bev arm, p=0.01). Objective response rate was 51.6% for FOLFIRI-Bev versus 41.2% for XELIRI-Bev (p=0.38). At the median follow-up of 24.5 months, the median progression-free survival (PFS) was not different between two groups (14.2 months in FOLFIRI-Bev vs. not reached in the XELIRI-Bev, p=0.30). However, median overall survival time for the FOLFIRI-Bev arm was better than that for patients treated with XELIRI-Bev, but these differences was not statistically significant (37.8 months vs. 28.7 months, respectively, p=0.58). Most commonly reported grade 3-4 toxicities (FOLFIRI-Bev vs XELIRI-Bev) were nausea/vomiting (7.8% vs. 14.7%, p=0.27), diarrhea (10.9% vs 22.1%, p=0.10), hand-foot syndrome (0% vs 8.8%, p=0.02) and neutropenia (18.7% vs 27.9%, p=0.22). Conclusion: Our results showed that FOLFIRI-Bev and XELIRI-Bev regimens were similarly effective treatments in a first-line setting for patients with untreated mCRC, with manageable adverse event profiles.