Abstract: Cambodian Phellinus linteus is a white rot fungus that behaves as a plant pathogen. This fungus was first used for studying changes in the wood chemistry and structure of Shorea (Shorea obtusa). Cambodian P. linteus comprises two different types of mycelia, namely monokaryon (n) and dikaryon (2n). Wood blocks of Shorea were exposed to monokaryons and dikaryons under in vitro condition and biodegradation took place over a 12-week-period. Shorea wood block degradation was determined by (1) wood weight loss (2) Fourier Transform Infrared (FTIR) and (3) Scanning Electron Microscopy (SEM). Results showed that the degradation of Shorea wood blocks by monokaryons and dikaryons was 57.48 and 55.73%, respectively. The FTIR analyses showed that the Shorea wood blocks degraded by the monokaryons and dikaryons were differed in their chemical components (aromatic, C-H and C-O). The results also suggested that the lignin and carbohydrates were decayed. Meanwhile, the C-O, C-O-H and C-H groups were decreased, revealing that hemicelluloses and cellulose polymers were broken down by hydrolytic enzymes during fungal growth. SEM was used to observe the physical changes of the Shorea wood blocks and it showed that the wood cells were changed. In conclusion, Cambodian P. linteus monokaryons are more appropriated for the paper industry (biopulping and bio-breaching) and enzyme technology than dikaryons, due to monokaryons leave no dark pigments and residues from the fruiting bodies. Moreover, monokaryons have a simple genetic system (n) for genetic and biochemical analyses.