A polyolefin composition suitable for preparing films and sheets, comprising: (A) from 15 to 40% by weight of a crystalline copolymer of propylene with at least one alpha-olefin of formula H.sub.2C.dbd.CHR.sup.1, where R.sup.1 is H or a C.sub.2-8 linear or branched alkyl, containing at least 90% by weight of propylene, having solubility in xylene at room temperature lower than 15% by weight; (B) from 60 to 85% by weight of an elastomeric fraction comprising: (1) a copolymer of propylene with ethylene, optionally containing 0.5 to 5% by weight of a diene, containing from 20 to 35% by weight ethylene, and having solubility in xylene at room temperature greater than 45% by weight, the intrinsic viscosity of the xylene soluble fraction ranging from 1.0 to 3.0 dl/g; and (2) a copolymer of ethylene with at least one alpha-olefin of formula H.sub.2C.dbd.CHR.sup.2, where R.sup.2 is a C.sub.2-8 linear or branched alkyl, optionally containing 0.5 to 5% by weight of a diene, containing 15% to 40% by weight alpha-olefin, and having solubility in xylene at room temperature greater than 35% by weight, the intrinsic viscosity of the xylene soluble fraction ranging from 1.0 to 3.0 dl/g; the (1)/(2) weight ratio ranging from 1:5 to 5:1. The polyolefin composition of the invention, preferably prepared by sequential polymerization in at least three stages, has a flexural modulus lower than 130 MPa, Shore D hardness lower than 40, and MFR.gtoreq.1.5 g/10 min.