Thermal inflation, a brief low energy inflation after the primordial inflation, resolves the moduli problem in supersymmetric cosmology. In the thermal inflation scenario, cosmological perturbations on large scales, corresponding to cosmic microwave background (CMB) or large-scale structure (LSS) observations, remain preserved, while perturbations on small scales tend to be suppressed. We show that the energy density and the potential shape of the moduli affect the power spectrum and discuss the possibility of probing the thermal inflation observationally.