Abstract: A composition comprising (a) poly-4-methylpentene-1 and (b) an olefin oligomer of the formula (I): ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4, which may be the same or different, each is a hydrogen atom or an alkyl group having up to 18 carbon atoms, and n represents the degree of polymerization and is such that the oligomer has an average molecular weight of about 200 to about 5,000, with the oligomer being present in the composition in an amount of about 0.5 to about 30 parts by weight per 100 parts by weight of poly-4-methylpentene-1.