Methanol extractives from moso bamboo (Phyllostachys pubescens) culms were found to have some regulation effects on the growth of the seed plants tested. They showed inhibition or promotion of hypocotyl and radicle growth of lettuce, watercress, and chrysanthemum. The methanol extractives were fractionated with n-hexane, diethyl ether, and ethyl acetate. The diethyl ether-soluble fraction contained more phenolic substances than the other fractions and showed strong inhibition of growth in lettuce seeds. The water-soluble fraction showed a promotion effect on the hypocotyl growth of lettuce. The water-soluble fraction was heated at 200°C for 8h, and the inhibition effect on the radicle growth of lettuce decreased and the promotion effect on the hypocotyl growth increased at 0.1% concentration.