Poly(ethylene-co-5.4 mol% n-alkyl/branched alkyl methacrylate)s (PEM) were prepared by a dehydrogenchloride reaction of poly(ethylene-co-5.4 mol% alkyl methacrylic chloride) with the corresponding alkyl alcohol to investigate effect of branching structure and length of alkyl ester on a few physical properties of PEM [glass transition temperature (T-g), degree of crystallinity in polyethylene region (X(c)) and dielectric molecular motion], where the alkyl groups used here are n-propyl, n-butyl, n-hexyl, n-decyl, 2-ethylhexyl, 3,5,5-trimethylhexyl and 2-(1’,3’,3’-trimethylbutyl)-5,7,7-trimethyloctyl. In the n-alkyl methacrylate copolymers, T-g and X(c) were almost unchanged with the presence of alkyl ester, but T-g increased and X(c) decreased in the highly branched alkyl methacrylate copolymers even at the low methacrylate content of 5.4 mol%.