The　adsorption　and　decomposition　of　acetonitrile　on　the　TiO2　(110)　surface　have　been　investigated　with　first　principles　calculations.　Our　results　reveal　that　both　C≡N　and　C-C　bonds　of　acetonitrile　become　weakened　after　adsorption.　Acetonitrile　behaves　as　an　electron　donor,　and　electrons　transfer　from　acetonitrile　to　substrate　is　obvious.　The　reaction　mechanism　of　further　decomposition　of　acetonitrile　on　TiO2　(110)　surface　is　also　investigated,　and　the　result　shows　that　acetonitrile　can　decompose　into　CH　3　and　CN　fragments　and　form　OCH3　and　NCO　groups　on　the　TiO2　(110)　surface,　which　consists　with　the　experimental　results.　©　2010　Wiley　Periodicals,　Inc.