Single　cell　gel　electrophoresis　assay　(SCGE),　also　named　as　alkaline　comet　assay,　was　a　simple,　rapid　and　sensitive　method　to　evaluate　DNA　damage.　In　this　study　SCGE　technique　was　used　to　monitor　DNA　damage　difference　in　tumor　patients　caused　by　chemotherapy,　DNA　damage　distribution　frequency　and　DNA　damage　characters　were　analyzed　by　komet　image　analysis　system　(KIAS).　The　results　showed　that　cyclophosphamide　greatly　caused　DNA　damage　in　lymphocytes　of　tumor　patients.　There　was　significant　difference　of　peripheral　blood　lymphocyte　DNA　damage　between　tumor　patients　and　healthy　controls.　Tail　length　of　lymphocytes　were　33.69　+/-　7.56　micro　m,　and　tail　DNA%　we　re　31.51　+/-　5.4　6%　in　10　cancer　patients　treated　with　cyclophosphamide,　while　Tail　length　were　1　6.2　+/-　1.5　micro　m　and　tail　DNA%　were　7.46　+/-　1.15%　in　healthy　controls.　there　was　great　significant　difference　on　tail　length　and　tail　DNA%　values　between　cancer　patients　and　healthy　controls　(P　＜　0.01).　In　conclusion,　the　successful　measurement　of　DNA　damage　caused　by　Cyclophosphamide　treatment　means　that　the　alkaline　comet　assay　as　a　valuable　tool　can　be　very　useful　in　cancer　epideminology　study,　and　also　be　valuable　to　evaluate　DNA　damage　status　of　patients　in　clinic.