Isobaric vapor-liquid equilibria (VLE) data for the four systems of dimethyl carbonate + ethylene carbonate, methanol + ethylene carbonate, dimethyl carbonate + ethylene glycol, and ethylene glycol + ethylene carbonate containing the carbonate group -OCOO-, which exist in the process of synthesizing DMC by transesterification of ethylene carbonate with methanol, have been measured at atmospheric pressure or under vacuum in an Ellis equilibrium still. The experimental VLE data are thermodynamically consistent, and the activity coefficients have been evaluated with the Wilson and NRTL equations, showing that the systems of dimethyl carbonate + ethylene glycol and ethylene glycol + ethylene carbonate have stronger nonideality. The results of this work are useful to the research on DMC synthesis by transesterification.