Three plant fragments were collected from two landslide profiles and were radiocarbon-dated by accelerator mass spectrometry. Results reveal that the two landslides occurred around AD 1646 and AD 1278, respectively. Mössbauer spectroscopy indicates that the sliding mud contains more ferrous iron species (para-Fe2+ and pyr-Fe2+) and less ferric iron (para-Fe3+ and hem-Fe3+) than do the overlying debris rock and the underlying bedrock. This suggests strong reductive condition within the slip zone relative to the underlying bedrock. Such a redox profile is different from the normal weathering profile whose oxidative conditions become reductive with increasing depth. The change of redox conditions in the sliding mud layer is most likely related to the percolated groundwater which is active in the slip zone.