Objective To detect the effect of formaldehyde on the activity of superoxide dismutase (SOD) and the concentration of malondialdehyde (MDA) in the lung tissue of the mice after they were made to inhale different amount of formaldehyde. Methods 36 mice were randomly divided into 6 groups, one of which was for control, and the other five were 20,40,60,80 and 100mg/m 3 dose group respectively.The mice were killed after they were given inhalation exposure of formaldehyde in a peaceful environment for 35 days,2 hours per day and then the activity of SOD and the concentration of MDA in the lung were measured. Results The activity of SOD in different dose groups was significantly lower than that of the control group, and the concentration of MDA were remarkably higher ( P <0 01). The activity of SOD and the concentration of MDA had no remarkable differences between the different dose groups( P >0 05), but the former showed an reduced activity, and the latter showed a higher concentration with the dosage up. Conclusion This study suggested that the activity of SOD and the concentration of MDA in the lung tissue of mice could change remarkably after they were given inhalation exposure of some amount of formaldehyde.