Abstract: The effects of pulsing electromagnetic fields (PEMFs) on cells are very important subjects in the field of bioelectromagnetics.In this experiment,the cytogene tic effects of PEMF on domestic pig lymphocytes were tested in vitro.Pig lymphocytes in RPMI 1640 medium were exposed to PEMFs of 100 kHz and 200 kHz for 12,24 and 48 hours.Chromosomal aberrations (aneuploidy,breaks,gaps,et al) were significantly increased in exposed cultures,and of these aberration s,56% chromosomal or chromatid breaks and 42% gaps induced by PEMFs were the points of pig chromosomal fragile sites.The baseline frequency of sister-chromati d exchange (SCE) increased after exposing lymphocytes continuously to PEMFs of 100 kHz and 200 kHz for 48 hours.These results suggested that the exposure to PEMFs might induce a type of DNA lesion and chromosomal aberrations.