Bacillus　cereus　LY-1　is　isolated　from　Indonesian　oil　sand　with　oil-sand　oil　as　the　only　carbon　source,　and　the　surfactant　secreted　by　bacteria　is　identified　as　lipopeptides.　GC　and　GC–MS　were　used　to　study　diesel　oil　degradation　by　B.　cereus　LY-1.　GC–MS　and　the　improved　B–L　method　were　used　to　study　the　changes　in　oil-sand　oil　composition　and　structural　parameters　due　to　bacterial　degradation.　The　results　of　GC–MS　show　that　the　main　volatile　components　of　diesel　oil　are　C11–C14　at　40℃,　and　B.　cereus　LY-1　has　higher　degradation　efficiency　for　saturated　alkanes　and　normal　alkanes　with　high　carbon　number　(C15–C24).　In　the　experiment　of　degrading　oil-sand　oil,　the　four　results　of　components　show　the　resin　in　the　treated　oil-sand　oil　is　reduced　from　60.41　±　1.03%　to　55.03　±　0.39%,　the　aromatic　fraction　increased　from　21.04　±　1.09%　to　23.42　±　0.7%,　and　the　saturated　hydrocarbon　fraction　increased　from　17.59　±　2.08%　to　21.55　±　0.44%.　The　results　of　GC–MS　show　that　after　B.　cereus　LY-1　treatment,　long-chain　saturated　alkanes,　aromatics,　and　complex　aromatics　can　be　utilized　by　B.　cereus　LY-1,　and　some　relatively　simple　complex　molecules　are　produced.　The　structure　of　oil-sand　oil　that　became　loose　further　illustrates　this.　The　oil　components　of　oil-sand　oil　are　converted　to　light　components,　and　B.　cereus　LY-1　has　the　ability　to　convert　complex　petroleum　hydrocarbons　into　relatively　simple　fatty　hydrocarbons.　©　2022,　Institute　of　Chemistry,　Slovak　Academy　of　Sciences.