Abstract: The field observation of suction in the landslide is very important for studying the criterion of the landslide instability induced by heavy rainfall in terms of the theory of unsaturated soil mechanics. It is essential to build a description of suction variation with depth in a landslide. For this purpose an observation well was constructed and observation data in almost half a year have been obtained. The analysis of these data gives us following ideas:Suction variation with depth in a landslide is controlled by the landslide structures and its material composition, and it is different from that described by some other authors.The variation of suction with rainfall in a landslide has a correspondence with primary rainfall at upper part of unsaturated zone, but the situation is quite different at middle and lower part of the unsaturated zone.