With　the　extensive　use　of　internal　combustion　engines,　the　large　volume　of　lubricant　consumption　has　become　an　urgent　problem.　In　this　study,　a　new　adsorbent　of　modified　sawdust　(MS)　was　used　to　clean　the　waste　diesel　engine　lubricant　and　prepared　into　a　pure　biomass　oil　filter　(PBF)　for　the　actual　operation　of　buses.　The　characterization　results　of　sawdust　showed　that　the　crystallinity　index　of　MS　enhanced　19.26%,　and　MS　had　smoother　morphology,　obvious　pores　than　raw　sawdust　(RS).　In　on-road　tests,　both　total　acid　number　(1　mg　KOH　center　dot　g(-1))　and　total　base　number　(9　mg　KOH　center　dot　g(-1))　were　within　the　permitted　range　of　the　standard,　and　the　kinematic　viscosity　showed　a　decreasing　trend.　In　addition,　the　concentration　of　metals　and　insoluble　colloids　(＜0.2%)　in　the　lubricant　was　far　below　the　oil　change　limit,　which　made　the　oil　drain　interval　of　the　two　vehicles　extended　from　15　000　km　(recommended　by　manufacture)　to　60　500　and　71　500　km,　respectively.　Conclusively,　it　is　believed　that　PBF　is　efficient　to　alleviate　lubricant　deterioration　and　prolong　the　oil　drain　interval.