Corncob,　an　agricultural　bio-waste,　was　used　as　adsorbent　to　remove　organic　and　inorganic　contaminants　in　waste　lubricating　oil　(WLO)　from　diesel　engine.　To　improve　its　adsorption　capacity,　corncob　was　modified　with　mixed　solution　of　nitric　acid,　Hexadecyl　trimethyl　ammonium　bromide　and　ethanol.　Characterization　results　showed　the　crystallinity　index　of　corncob　enhanced　12%,　which　would　be　ascribed　to　the　disruption　of　the　dense　lignin-carbohydrates　structure　in　lignocellulose　biomass　by　modification.　The　surface　of　modified　corncob　became　smoother　and　porous.　The　adsorption　results　showed　modified　corncob　had　better　removal　rates　to　contaminants　than　raw　corncob.　For　WLO　with　80,000　km　mileage,　the　removal　rates　to　Fe,　Al,　Cu　were　enhanced　from　19%,　6.4%,　48-27%,　27%,　53%,　while　that　for　oxide,　sulphate,　aromates,　soot　and　insoluble　resins　were　enhanced　1.7,　1.2,　3.0,　1.7　and　1.7　times.　The　reduction　rate　of　total　acid　number　to　WLO　with　40,000,　60,000,　80,000　km　were　enhanced　16%,　9%,　12%　by　modified　corncob,　respectively.　The　optimal　adsorption　condition　was　explored　as　adsorbing　60　min　at　90　degrees　C　with　2%　adsorbent.　Corncob,　with　the　advantages　of　low　cost,　good　biodegradability　and　high　adsorption　capacity,　could　be　used　as　alternative　to　conventional　adsorbent　for　WLO.