  We consider supersymmetric model with Peccei-Quinn symmetry and study effects
of saxion on the evolution of the universe, paying particular attention to the
effects of thermal bath. The axion multiplet inevitably couples to colored
particles, which induces various thermal effects. In particular, (i) saxion
potential is deformed by thermal effects, and (ii) coherent oscillation of the
saxion dissipates via the interaction with hot plasma. These may significantly
affect the evolution of the saxion in the early universe.
