We investigated the reflectances of black plant fragments in melanic Andisols and of fresh charcoal produced during modern grassland and forest fires with the aim of clarifying the origin of fragments in melanic Andisols. The reflectance values of most Andisol plant fragments were less than 2%; all values were below 3%. These values are considered to have formed at temperatures of at least 200°C, indicating that these fragments are charcoal fragments. The reflectances of the fragments in melanic Andisols were similar to those of grass charcoal from grassland fires rather than wood charcoal produced during forest fires. This finding indicates that most charcoal fragments in melanic Andisols are the product of grassland fires. The small difference between the reflectance values of the charcoal fragments in the Andisols and the grass charcoal is possibly derived from the fact that charcoal fragments with lower reflectance are more likely to be retained in the soil than fragments with higher reflectance values.