A polyolefin composition having good transparency and mechanical properties comprising, all percent amounts being by weight: A) from 70 to 98% of a propylene homopolymer or copolymer having haze of 25% or less and melting temperature of 130° C. or higher; and B) from 2 to 30% of a butene-1 copolymer containing from 0.5 to 30% of one or more comonomer(s).