Abstract: Objective To explore damage effect of fish sauce and nitrosated fish sauce on DNA in gastric epithelial cell.Methods The DNA damage effect of fish sauceong astric epithelial cell was observed in vitro and in vivo by improved single cell gel electrophoresis assay.Results The tail length,tail moment and OLIVE tailmomentin for nitr osated fish sauce groups of high dose(13.42±3.74),(1.12±0.67),(1.21±0.71)μm,middle dose(12.68±4.44),(1.07±0.68),(1.12±0.69)μmand low dose(11.79±4.49),(0.98±0.72),(1.05±0.70)μmwere significantly higher than those in control group(9.14±2.54),(0.62±0.60),(0.60±0.59)μmin vitro.There were statistical differences between any two groups(χ_tailength²=296.10;F_tailmoment=27 62;(χ_{OLIVE tailmoment}² =436.62;P<0.01).And in vivo the taillength,tailmoment and OLIVE tailmoment in the groups of 50% nitrosated fish sauce(14.51±4.54)(2.76±2.26)(3.03±2.32)μm and 25%nitrosated fish sauce(13.49±4.42)(2.06±1.86)(2.25±1.98)μmwere hig her than those in control group (11.82±3.80)(1 12±0.80)(1.35±1.19)μm.There were also statistical differences between any two groups(χ_tailength²=88.11;χ_tailmoment=165.83;χ_tailmoment=198.11;P<0.01).And in vitro the higher the concentration of nitrosated fish sauce was,the stronger the damage effect of DNA was.There was dose-response relationship(r_tailength=0.999,P<0.05,r_{OLIVE tailmoment}=0.997,P<0.05).Conclusion Fish sauce exists damage effect on DNA in gastric epithelial cell through ni trosation.