Because　of　the　micromachining　characteristic　of　excimer　laser　ablation,　the　microchannels　ablated　with　this　technique　on　poly(methyl　methacrylate)　(PMMA)　substrate　have　definite　surface　roughness.　Utilizing　this　characteristic,　the　hydrophilicity　of　PMMA　microchannels　could　be　directly　modified　during　fabrication　process　both　by　the　mechanism　of　photochemical　ablation　and　the　effect　of　surface　roughness.　The　contact　angle　is　inversely　proportional　to　the　surface　roughness　under　ablation　with　same　fluence　and　could　be　reduced　to　25　degrees　by　choosing　ablation　parameters　reasonably　(7.38　J/cm(2),　20　Hz,　10　mm/min).　Excimer　laser　irradiation　of　PMMA　substrates　for　different　irradiation　times　at　fluence　below　the　ablation　threshold　also　results　in　the　surfaces　becoming　more　hydrophilic　without　any　marked　change　in　the　surface　topography.　The　contact　angle　decreases　with　the　increase　of　irradiation　times　and　finally　reaches　the　saturated　status　after　irradiation　for　2,500　times.　Under　same　irradiation　times,　higher　fluence　led　to　PMMA　substrates　more　hydrophilic.