The temperature dependence of the molar heat capacity C o p,m of butylmethacrylate and perdeuterobutylmethacrylate in crystalline, glassy, overcooled liquid, and liquid states has been studied at temperatures between 10 K and 330 K in a vacuum adiabatic calorimetric cryostat within ±0.002· C o p,m . The temperature and enthalpy of melting of the compounds have been measured. The quantities of the glass transition and the glassy state such as the glass-transition temperature T o gt, the increase in heat capacity on devitrification Δ C o p,m ( T o gt), the zero-temperature entropy S o gt(0), the configurational entropy S o conf, and the difference in zero-temperature enthalpies of the substances in glassy and crystalline states { H o gt(0) - H o cr (0)} have been determined. From the values obtained, the thermodynamic functions: Δ T 0 H o m, Δ T 0 S o m, and Φ o m have been calculated from T → 0 to 330 K. From the enthalpies of formation of polybutylmethacrylate and polyperdeuterobutylmethacrylate obtained from enthalpies of combustion of the polymers in highly elastic states at T = 298.15 K and p = 101.325 kPa as well as the enthalpies of polymerization of the monomers in bulk measured by direct calorimetry, the standard enthalpies of formation Δ f H o m of liquid butylmethacrylate and perdeuterobutylmethacrylate have been estimated. For the same physical states the standard molar entropies of formation Δ f S o m and the standard molar Gibbs function of formation Δ f G o m for the compounds have been calculated. The quantitative influence of the substitution of hydrogen for deuterium on the thermodynamic properties of butylmethacrylate has been revealed.