Objective To investigate acute cell damage and delayed inhibition effects by pulsed electric fields(PEFs)with different frequencies on human ovarian carcinoma cell line SKOV3 in vitro and in subcutaneous transplanted tumor of human SKOV3 in BALB/c nude mice,and evaluate the potential use of relatively higher frequency PEFs to reduce unpleasant sensations without decreasing therapeutic effects in clinical electrochemotherapy.Methods Firstly,SKOV3 cell suspension were exposed to PEFs with gradient increasing frequencies(1,60,1 000,5 000 Hz)and voltages(50,100,150,200,250,300,350,400 V),respectively.MTT assay was used to determine the acute cell damage.Then PEFs with gradient increasing frequencies(1,60,1 000,5 000 Hz)and fixed voltage (250 V)were applied to the subcutaneously transplanted tumor,in vivo antitumor assay was used to observe the delayed inhibition effect;histological changes were observed by light and electron microscope. Results The 1 Hz PEFs has similar cytotoxic effects with 5 kHz,and no significant difference of delayed tumor inhibition effect on subcutaneous transplanted tumor among all groups exposed to different frequencies of PEFs(P＞0.05).Histological observation showed acute damage in all exposed groups.and only in 5 kHz group was induced apoptotic effect observed.Conclusions PEFs with relatively higher frequency can achieve similar tumor killing effect with the low frequency PEFs,and it can also induce apoptosis.Relatively higher frequency PEFs show therapeutic potentials for reducing unpleasant sensations in clinical electrical treatment of tumor.