Objective　To investigate the mechanism of lipid peroxidation by which chrysotile fibres exert their effect in human in vivo and in vitro.Methods　Plasma malondialdehyde (MDA, an indicator of lipid peroxidation) and activities of superoxide dismutase (SOD) and glutathion peroxidase (GSH-Px) were determined in 47 female workers, who were exposed to high airborne concentration of chrysotile fibres (mean 18.40±3.23, ranging from 5.0～186.3 mg/m3), 12 female asbestosis patients with simple asbestosis and controls. Meanwhile MDA level and SOD activity in cell membrane were detected in macrophages treated by chrysotile fibres.Results　Plasma MDA level and activities of SOD and GSH-Px of exposed female workers were 3.23±0.59 μmol/L, 17.39±4.63 U/ml, 181.61±12.49 U/L, respectively. Likewise those of non-exposed controls were 2.15±0.75 μmol/L, 11.99±3.99 U/L, 170.13±15.12 U/L respectively. Plasma MDA level and activities of SOD and GSH-Px of exposed female workers were significantly higher than those of the non-exposed controls (P<0.001). While, mean plasma MDA and SOD, GSH-Px of the asbestosis　patients (mean 3.03±0.71 μmol/L,18.23±6.97 U/ml, 180.04±7.73 U/L, respectively) and those of chrysotile-exposed controls (mean 2.77±1.54 μmol/L, 17.44±4.47 U/ml, 182.52±6.61 U/L, respectively) were not significantly different (P>0.05). Correlations between plasma MDA and durations of exposure among asbestos exposed workers were statistically insignificant: γ=-0.1934, P>0.05. Moreover, it existed a balance between MDA level and SOD activity with MDA levles increasing and SOD activity decreasing. While SOD was feedbackly increasing and MDA decreasing, the MDA was then increasing gradually and SOD decreasing. The process occurred progressively. At the same time, chrysotile fibres could elevate MDA level and decrease SOD activity in the cell membrane of macrophages at the concentrations of 100 μg/ml in vitro.Conclusions　The results suggest the involvement of lipid peroxidation on exposure to chrysotile fibres and development of antioxidant mechanisms in exposed workers and asbestosis patients, and support the opinion that LPO plays an important role in the development of asbestosis, and MDA and antioxidase, such as SOD, porbably constitute sensitive features of prediction and trending observation.