  We discuss effects of cosmological moduli fields on the cosmic microwave
background (CMB). If a modulus field \phi once dominates the universe, the CMB
we observe today is from the decay of \phi and its anisotropy is affected by
the primordial fluctuation in the amplitude of the modulus field. As a result,
constraints on the inflaton potential from the CMB anisotropy can be relaxed.
In addition, with the cosmological moduli fields, correlated mixture of
adiabatic and isocurvature fluctuations may be generated, which results in
enhanced CMB angular power spectrum at higher multipoles relative to that of
lower ones. Such an enhancement can be an evidence of late time entropy
production due to the cosmological moduli fields, and may be observed at
on-going and future experiments.
