Syndiotactic propylene-ethylene copolymers have been synthesized with a single-center C,symmetric syndiospecific metallocene catalyst. The samples show novel thermoplastic elastomeric behavior. Samples with ethylene contents lower than 18-20 mol % are crystalline and show high ductility and remarkable values of the tensile strength. Unoriented compression-molded films of the most crystalline samples, with ethylene contents lower than 6-7 mol %, show poor elastic properties, as in the case of syndiotactic polypropylene, but higher ductility. The elastic properties are improved with increasing ethylene concentration. Stress-relaxed oriented films, instead, present good elastic properties regardless of ethylene concentration. For the most crystalline samples, with ethylene contents lower than 6-7 mol %, the elastic behavior is associated with a reversible polymorphic transition between the trans-planar form III and the helical form II that provides an enthalpic contribution to the elasticity. For less crystalline samples, with higher ethylene concentration, the elastic recovery is not associated with any polymorphic transitions and has a pure entropic origin, as in conventional elastomers.