Properties of vinyl chloride-ethylene copolymers rich in vinyl chloride have been studied by means of infrared as well as NMR spectroscopy and dynamic mechanical testing. The infrared and NMR spectra of the copolymer indicate that crystallinity decreases with decreasing sequence length of the vinyl chloride segment. The copolymer containing more than 80 mol % vinyl chloride shows optical melting point, a plot of which versus logarithmic composition satisfies Flory’s relationship. Temperature dispersion curve of elastic modulus E′ of the copolymer also indicates that the crystalline region of vinyl chloride segments disappears as the ethylene content increases. Glass transition temperature as determined by loss modulus E″ fits Gordon-Taylor’s relationship well provided the coefficient k equals unity.