  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. Consequently,
constraints on the inflaton potential from the CMB anisotropy can be relaxed.
In particular, the scale of the inflation may be significantly lowered. 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 the cosmological moduli fields, and
may be observed in future satellite experiments.
