Abstract: Vast loss of timber resources can be reduced by preventing and controlling the decay of standing trees in forest management. Therefore,  research concerning the effect of site conditions on decay of standing trees is particularly important for decay prevention and cure. A relevant study was carried out in Xiaoxing’anling Mountains on October, 2013, and thirty decayed and ten normal mature or postmature Korean pine (Pinus koraiensis) live standing trees were selected as sample trees, respectively. Two increment core samples were selected from the basal trunk of each sample tree to measure the mass loss ratio of rotted increment core samples. Meanwhile, moisture content of the soil near sample trees’ roots and the gradient, exposure, slope position and elevation of the site where sample trees located were tested or measured. Analysis was made upon the relationship between factors such as sapwood and heartwood moisture contents and the decay of sample trees by correlation analysis and analysis of variance. The results indicated that moisture content of the sapwood negatively correlated with the decay degree of Korean pine live standing trees at a very significant level, so did the heartwood moisture content. Soil moisture content had a positive correlation with the decay degree at a highly significant level. Significant differences  in the moisture contents of sapwood, heartwood and soils were observed between decayed and normal sample trees. Slope position was the only factor that had a significant effect on the decay degree among all the three slope factors. The decay degree of live standing trees on the middle part of slopes was significantly higher than that on the upper part of slope, mainly due to the significantly higher soil moisture content on the middle part of slope. Elevation of the site where sample trees located had no significant correlation with the decay degree of Korean pine.