AbstractThe main chemical indicators for healthy wood and rotted wood at different decay levels in two species, namely Juglans mandshurica Maxim. and Pinus koraiensis, were preliminary analyzed. The cellulose content, lignin content, and relative crystallinity were measured using the nitric acid-ethanol method, acid-insoluble lignin, and X-ray diffraction to further explore the process of wood decay. Results indicated that the cellulose content and relative crystallinity decreased and the acid-insoluble lignin content increased as wood decay increased. X-ray diffraction results showed that there were no significant changes in the lattice structure between healthy wood and rotted wood. Approximately 98.3% and 99.9% of the variations in wood decay for Juglans mandshurica Maxim. and Pinus koraiensis, respectively, can be explained by the comprehensive effect of the above chemical indicators.