Abstract: ObjectiveTo investigate the efficacy and safety of S1 combined with oxaliplatin as firstline treatment for metastatic colorectal cancer（mCRC）. 
MethodsA wide search of randomized clinical trials （RCT）using S1 combined with oxaliplatin as a firstline therapy for mCRC patients was performed in the Cochrane Library， PubMed， EMBASE， MEDLINE， CNKI and WanFang databases. All included studies were assessed according to the guidance of the Cochrane Collaborations tool for assessing risk of bias of RCTs， and then statistical analyses were performed using Rev Man 53 software. 
ResultsA total of 5 RCTs involving 1382 patients were included. Meta analysis indicated that the progressionfree survival（HR=0.90，95％CI：0.801.02，P=0.10）， overall survival（HR=1.14，95％CI：0.981.31，P=0.08）， objective response rate（RR=1.12，95％CI：0.871.43，P=0.38）， disease control rate（RR=104，95％CI：0.981.10，P=0.24）， showed no statistical significance between S1 combined with oxaliplatin and oxaliplatin combined with 5FU or capecitabine. For side effects， S-1 combined with oxaliplatin could decrease incidence of grade 34 leukopenia， but increased the incidence of grade 3.4 stomatitis， anorexia， diarrhea. There were no statistical difference between the two regimen in the incidence of neutropenia， anemia， thrombocytopenia， nausea， vomiting and fatigue. 
ConclusionS1 combined with oxaliplatin seem to have similar efficacy in the firstline treatment for mCRC with different toxicity. The S-1 may offer an alternative to 5-FU.

Key words: Metastatic colorectal cancer, S-1, Chemotherapy, Metaanalysis