The　objective　of　this　study　was　to　explore　the　O-6-methylguanine-DNA　methyltransferase　(MGMT)　gene　methylation　status　and　its　protein　expression,　as　well　as　the　effects　of　demethylating　agent　5-Aza-2＇-deoxycytidine　(5-Aza-CdR)　on　MGMT　gene　expression　and　its　resistance　to　alkylating　agents,　and　to　elucidate　MGMT　expression　mechanism　and　significance　in　osteosarcoma.　The　human　osteosarcoma　cell　lines　Saos-2　and　MG-63　were　collected　and　treated　with　5-Aza-CdR　for　6　days.　The　cells　not　treated　with　5-Aza-CdR　were　set　as　a　negative　control.　The　genomic　DNA　was　extracted　from　the　Saos-2　and　MG-63　cells　using　methylation-specific　PCR　to　detect　the　promoter　CpG　island　methylation　status　of　the　MGMT　gene.　Cell　sensitivity　to　alkylating　agents　before　and　after　drug　administration　was　detected　by　the　MTT　method.　The　variation　in　MGMT　gene　mRNA　and　protein　was　detected　by　reverse　transcription　PCR　(RT-PCR)　and　Western　blotting.　The　MGMT　promoter　gene　of　normal　Saos-2　cells　was　methylated,　with　reduced　MGMT　mRNA　and　protein　expression;　the　MGMT　mRNA　and　protein　expression　of　Saos-2　cells　treated　with　5-Aza-CdR　was　obviously　enhanced,　and　its　sensitivity　to　alkylating　agents　was　reversed.　Meanwhile,　with　promoter　CpG　island　unmethylation　of　the　MGMT　gene,　MGMT　protein　was　expressed　in　the　normal　MG-63　cells　and　the　MG-63　cells　treated　with　5-Aza-CdR,　and　both　showed　resistance　to　alkylating　agents.　The　methylation　status　of　the　MGMT　gene　promoter　in　human　osteosarcoma　cells　reflected　the　cells＇　ability　to　induce　MGMT　protein　expression　and　can　be　used　as　a　molecular　marker　to　project　the　sensitivity　of　cancer　tissues　to　alkylating　agent　drugs.