Surface　tension　inherently　exists　on　free　surface,　and　its　effect　becomes　quite　important　at　sharp　crack　tip.　In　the　present　paper,　we　investigate　the　influence　of　surface　tension　on　mixed-mode　cracks　by　finite　element　method.　It　is　found　that　surface　tension　significantly　alters　the　stress　fields　and　J-integral　around　crack　tip,　depending　on　the　profile　of　crack　tip.　Generally,　surface　tension　decreases　the　J-integral　and　thus　enhances　material　toughness,　especially　for　sharp　crack.　Based　on　the　criteria　of　energy　release　rate,　the　critical　stress　intensity　factor　(SIF)　for　brittle　materials　is　also　determined.　Surface　tension　yields　an　enhanced　critical　SIF　for　mixed-mode　cracks,　and　more　significant　strengthening　effect　is　obtained　for　Mode-I　crack　than　for　Mode-II　crack.　Moreover,　an　analytical　expression　is　advanced　to　characterize　the　influence　of　surface　tension　on　fracture,　which　shows　a　good　agreement　with　numerical　calculations.