The structural characterization of syndiotactic copolymers of propene with I-butene, prepared with a single-center metallocene-based catalyst, is reported. The copolymers are crystalline in a whole range of comonomer composition. The increase of a and b axes of the unit cell from the values of syndiotactic polypropylene to those of syndiotactic poly(l-butene), with increasing content of I-butane, indicates that the comonomeric units, propene or l-butene, are included in the unit cells of both homopolymers. As-prepared copolymers having small contents of l-butene are crystallized in a structure similar to that of form I of syndiotactic polypropylene, although disorder in the alternation of right and left-handed helical chains along both axes of the unit cell and in the stacking of be layers of chains piled along a (b/4 shifts disorder) is present. With increasing content of I-butene, the amount of b/4 shifts disorder increases and disordered modifications having structures intermediate between the limit-ordered models of form I of syndiotactic polypropylene and form I of syndiotactic poly(l-butene) are obtained. Samples with a content of l-butene higher than 70-80 mol % crystallize in a structure similar to that of form I of syndiotactic poly(l-butene) (as well as of form II of syndiotactic polypropylene).