The spectroelectrochemical properties of manganese phthalocyanine (MnPc) thin films are studied. Cyclic voltammetry (CV) and UV-vis in situ spectroelectrochemistry were done to characterize the MnPc thin films. In this study, the insertion of cations during the reduction of MnPc thin films is proposed. Two reversible redox pairs were observed at 0 and - 0.9 V (vs. Ag \ AgCl) as judged by CVs. According to the absorption spectral data, the reaction at 0 V is related to the transformation between [(MnPc2-)-Pc-III] and [(MnPc2-)-Pc-II], and the reaction at -0.9 V is attributed to the transformation between [(MnPc2-)-Pc-II] and [(MnPc2-)-Pc-I]. The polychromic characteristics of MnPc thin films were also observed under different redox potentials and can be expressed as follows: 0.5 (light green) --> -0.5 (green) --> -0.9 (greenish blue) --> -1.0 V (purple). The electrochromism of MnPc thin films for use in electrochromic devices (ECD) is also discussed. A complementary ECD, comprising a MnPc and polyaniline (PAni) thin film couple was constructed. This device was darkened and bleached using - 1.0 and + 1.0 V, respectively, The color of the device was changed from light green to green and the transmittance of the device varied from 60 to 17% at 550 nm.