For　the　microfluidic　chip,　the　surface　roughness　of　the　chamber　sidewall　is　an　important　parameter　in　estimating　its　quality.　In　this　work,　the　chambers　of　the　polymethyl　methacrylate　(PMMA)-based　microfluidic　chip　were　fabricated　by　CO2　laser　cutting,　and　then　the　surface　roughness　of　the　sections　cut　using　different　laser　parameters　and　ambient　temperature　was　studied　by　a　non-contact　3D　surface　profiler.　Our　observation　shows　that　the　surface　roughness　results　primarily　from　the　residues　on　the　laser-cut　edge,　which　are　produced　by　the　bubbles　bursting.　To　reduce　the　surface　roughness　of　the　cut　section,　a　new　approach　is　proposed,　that　is　preheating　the　PMMA　sheet　to　a　suitable　ambient　temperature　during　laser　processing.　The　results　indicate　that　at　a　preheat　temperature　of　70-90　degrees　C,　the　surface　roughness　resulting　from　the　cut　would　be　reduced.　In　our　experiment,　the　best　result　was　that　the　arithmetical　mean　roughness　is　R-a　=　100.86　nm　when　the　PMMA　sheet　was　heated　to　85　degrees　C.　(C)　2009　Elsevier　B.V.　All　rights　reserved.