Abstract: Abstract: Objective To study the effect of rotary magnetic field (RMF) combining 5-Fu on the cycle and apoptosis of mouse cell line SP2/0 in vitro. Methods SP2/0 cells were randomly divided into four groups: control group (N), 5-Fu group (C), magnetic group (M) and magnetic combining 5-Fu group (M+C).The M and M+C groups were treated with a RMF for two hours once a day.On day 4, the C and M+C groups were treated with 5-Fu 20 μg/ml.On day 5, cell cycle and apoptosis were measured by the flow cytometric (FCM). Results The S phase proportion of the M group and the G1 phase proportion of the C group were higher than that of the other three groups（P<0.05）.The S phase proportion of the M+C group decreased and lower than that of the M group，but was still higher than that of the N and C groups（P<0.05）.There was no significant difference in apoptosis rates between the N and M groups（P>0.05）.The apoptosis rates of the C and M+C groups were remarkedly higher than those of the N and M groups and the M+C group had the highest apoptosis rate. Conclusion The RMF can't induce the apoptosis.But it can enhance the cytotoxicity of 5-Fu and promote the cell apoptosis.The mechanism of the apoptosis may be related to SP2/0 cell line arrested at S phase.