The single cell gel electrophoresis (SCGE), also called comet assay, is a simple,rapid and sensitive biochemical technique for detecting DNA single strand breakage of the mammalian cells. In order to study the anti-cancer mechenism of CM4-component of the anti-bacterial peptides (CM4-ABP), the SCGE was used to observe the chromatin DNA breakage action of the K562 cancer cells comparing with the leucocytes of normal human under treating with CM4-ABP.Using the fluorescent microscopy, it is observed the chromatin DNA cleavage of the K562 cancer cells treated with CM4-ABP forms brighte fluorescent head and comet like tail; On the contrary, the normal human leucocytes treated and the K562 cancer cells untreated with CM4-ABP show intact, round nuclei, no comet tails. The analysis of comet assay showed that the averge ratio of the K562 nuclei cleavage is 73.62% (P＜0.001). The results showed that the CM4-ABP can cause the chromatin DNA of the K562 cells damaged, but it has no normal human leucocytes.