Metallocene-catalyzed copolymers of ethylene and alpha-olefins were investigated by X-ray scattering and differential scanning calorimetry. Evaluated alpha-olefin comonomers consisted of 8, 12, 18, or 26 carbons. As indicated from the small-angle X-ray scattering, ethylene-hexacosene copolymer with comonomer content of 3 mol % may contain second crystallites. Because no other reflections were observed in the wide-angle X-ray scattering patterns, the side-chain crystallites should have the same crystal lattice dimensions as the prevailing main-chain crystallites. Since this potential side chains crystallization can only be found in the ethylene-hexacosene copolymer with 3 mol % of comonomer, a critical concentration oflong-chain comonomer should be reached for this secondary crystallite formation. It was also found that the thickness of the interlamellar amorphous layer stays virtually constant regardless of the changes in comonomer content and side-chain length.