The　conversion　of　lignocellulose　into　a　value-added　chemical　with　high　selectivity　is　of　great　significance　but　is　a　big　challenge　due　to　the　structural　diversities　of　biomass　components.　Here,　we　have　reported　an　efficient　approach　for　the　one-step　conversion　of　raw　lignocellulose　into　diethyl　maleate　by　the　polyoxometalate　ionic　liquid　[BSmim]CuPW12O40　in　ethanol　under　mild　conditions.　The　results　reveal　that　all　of　the　fractions　in　biomass,　i.e.,　cellulose,　lignin　and　hemicellulose,　were　simultaneously　converted　into　diethyl　maleate　(DEM),　achieving　a　329.6　mg　g-1　yield　and　70.3%　selectivity　from　corn　stalk.　Importantly,　the　performance　of　the　ionic　liquid　catalyst　[BSmim]CuPW12O40　was　nearly　twice　that　of　CuHPW12O40,　which　can　be　attributed　to　the　lower　incorporation　of　the　Cu2+　site　in　[BSmim]CuPW12O40.　Hence,　this　process　opens　a　promising　route　for　producing　bio-based　bulk　chemicals　from　raw　lignocellulose　without　any　pretreatment.　©　2021　The　Royal　Society　of　Chemistry.