Reflectance factors were estimated using 8 Thematic Mapper images, and seasonal spectral changes of deciduous and evergreen cool temperate forests were examined from the reflectance factors. Our findings were as follows. 1) The seasonal changes were similar in channel 1 (blue) and 3 (red) in each forest. Deciduous forests had higher reflectance factors during the defoliated periods in early spring and late autumn. However, the reflectance factors decreased in the growing season due to the presence of green leaves. Evergreen forests showed stable reflectance factors from early spring until late autumn. 2) In deciduous forests, the highest reflectance factors in channel 2 (green) appeared in late spring. In evergreen forests, the reflectance factors in channel 2 and 4 (near infrared) peaked at the same time. 3) The reflectance factors in channel 4 increased greatly in late spring, and started to drop in mid-summer. Leaf development may appear most clearly in this channel. 4) In evergreen forests, reflectance factors in channel 5 (middle infrared) were highest in mid-summer and lower in early spring and late autumn. In deciduous forests, reflectance factors in channels 5 and 7 (middle infrared) were higher in late spring and decreased until just before defoliation.