We analyzed the physicochemical and spectroscopic properties of three charred plant fragments (CPF) that were isolated from three volcanic ash soils in Japan. Values of δ13C showed that the CPF originated from C3 and C4 plants. The contribution ratio of C4 plants to the CPF was much higher in Soils 1 and 3 than in Soil 2. Values of δ15N of the CPF were higher in Soil 3 isolated from the deeper soil horizons. Light reflectance values suggested that part of the CPF experienced combustion temperatures higher than 400°C in Soil 2 and less than 400°C in the other soils, respectively. Atomic [H]/[C] and [O]/[C] ratios suggested that the CPF were subjected to weathering (oxidative degradation and hydrolysis) in soil for a long period after burning. The degree of weathering was considered to be larger in Soils 1 and 3. Spectra of 13C-NMR of the CPF, except the area of alkyl-C, were similar. Infrared (IR) spectra of three CPF, except aliphatic C-H stretching, were also similar to each other. The X-ray diffraction patterns of the CPF in Soil 2 clearly revealed the presence of graphite-like structure. From these findings, it was assumed that the physicochemical and spectroscopic characteristics of the CPF were strongly influenced by the type of burnt vegetation.