This study investigates the cooperative molecular dynamics of poly(vinyl methyl ether) (PVME) at temperatures above and below the glass transition temperature, T-g, using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The DSC measurements of PVME aged at temperatures below T-g revealed the aging-time-dependent enthalpy relaxation. The BDS measurements revealed the structural alpha-relaxation process that originated from segmental chain motion at temperatures above T-g. Both the enthalpy and dielectric relaxation are described via a stretched exponential function, exp(-(t/tau)(beta K)), and the relaxation time, tau, and the stretching index, beta(K), are obtained. tau and beta(K) of the enthalpy relaxation obtained via DSC measurements are compatible with those of the structural alpha-relaxation obtained via BDS measurements. This similarity indicates that the molecular origin of the enthalpy relaxation is the same as that of the dielectric alpha-relaxation process of the polymer, i.e., its segmental chain motion.