Rock-magnetic and palaeomagnetic studies have been carried out on the interval of famous fossil-bearing sedimentary rocks and its overlying basalts and underlying basalts at the Sihetun section, West Liaoning Province. Normal polarity was obtained for the sedimentary interval and the underlying basalts, while reversed polarity was found in the overlying basalts. Taking account of the new 40Ar/39Ar ages (Swisher et al., 1999), we classified the fossil-bearing sedimentary interval into the Barremian M3n zone (Early Cretaceous age). Several abnormal horizons on magnetic properties, probably corresponding to the tuffs, were observed in the fossil-bearing sedimentary interval. This implies that the massive bio-extinction may link to dramatic environmental changes that were caused by volcanic eruptions. Rock-magnetic and palaeomagnetic studies have been carried out on the interval of famous fossil-bearing sedimentary rocks and its overlying basalts and underlying basalts at the Sihetun section, West Liaoning Province. Normal polarity was obtained for sedimentary interval and the underlying basalts, while Taking account of the new 40Ar / 39Ar ages (Swisher et al., 1999), we classified the fossil-bearing sedimentary interval into the Barremian M3n zone (Early Cretaceous age). Several abnormal horizons on Magnetic properties, probably corresponding to the tuffs, were observed in the fossil-bearing sedimentary interval. This implies that the massive bio-extinction may link to dramatic environmental changes that were caused by volcanic eruptions.