ObjectiveTo study the reaction of Guizhou miniature pig to the DNA damage and repair caused by chemical substances or drugs. MethodsSingle cell gel electrophoresis was used to study the DNA damage and repair caused by 5 -azacytidine(5 -azaC) in phytohemagglutinin (PHA) -stimulated and unstimulated lymphocytes. Results5 -azaC induced significant DNA migration(comet tail) in unstimulated lymphocytes, and the DNA migration after 2h repair incubation was of no significance compared with pre -incubation. In contract, the comet tail induced by 5 -azaC significantly reduced after 2h repair incubation compared with pre -incubation. ConclusionThe DNA damage caused by 5 -azaC in unstimulated lymphocytes of Guizhou miniature pig was not significantly repaired within 2h post -incubation, but significantly repaired in PHA -stimulated cells.