Forest fires can disturb the evolution of plant communities and influence both soil organic matter (SOM) and soil physicochemical properties. The historic vegetation changes and the influences on soil properties and OM induced by fires are still not well known for central Taiwan. This study investigates the effect of forest fires on SOM and soil physicochemical properties, as well as vegetation changes, in two parallel burnt and unburnt stands of pine and mixed forest. Fresh plant tissues and four pedons of the selected stands were subjected to physical, chemical, and mineralogical analysis of the soils, as well as cross-polarization and magic angle spinning 13C-nuclear magnetic resonance spectroscopy to determine the functional groups of SOM. Soil textures from the four pedons ranged from clay to silty loam. Soil pH ranged from 3.68 to 5.28 and increased with increasing soil depth. Illite, kaolinite, and vermiculite were the major clay minerals identified by the X-ray diffraction analysis. The organic functional groups of the mixed forest stand SOM showed a trend similar to that of the pine forest stand, containing high hemicellulose and lignin materials. High aromatic C contents were observed in the burnt zones. In this study site, the δ13C values of the OM from Pedons 1 and 2 of the unburnt and burnt pine stands were compared with those of mixed forest stands (Pedons 3 and 4). The recent forest fires did not seriously interfere with the SOM contents. It can be seen that the variations of δ13C values in the forests are caused by high soil erosion on the steep slopes.