Abstract: Objective To study the effect of ultra strong static magnetic field(USMF) on gene expressions of catalase (CAT) and glutathione peroxidase(GSHPx) in mice.Methods One-week-aged mice were exposed to USMF at 12 Tesla (T) for 8,12 or 16 hours.Total liver RNAs was then extracted.Expression levels of CAT mRNA and GSH-Px-mRNA were mea sured with quantitative RTP-CR6 12 or 24 hours after the exposure.Results CAT-mRNA and GSH-Px-mRNA levels in 12hr-treated mice incresed to 1.154 and 0.881(optical absorption ratio) without significant increase compared to those of the controls.CAT-mRNA and GSH-Px-mRNA levels in 16hr-treated mice was upregulated (1.112 and 0.887,optical absorption ratio) 6 hours after the exposure.Conclusion Gene expressions of CAT and GSH-Px,the markers of antioxidant ability,are not impaired by 12TUSMF treatment in mice.