Abstract: A catalyst for polymerization of an olefin, is provided which contains a solid catalyst component (A) obtained by supporting a transition metal compound having formula (1): ##STR1## onto a solid inorganic compound, and then washing the solid inorganic compound with a nonaqueous solvent capable of dissolving the transition metal compound, where M is a transition metal of Group 4b; X.sup.1 and X.sup.2 are, independently, a halogen, hydrogen, an alkylalkoxy group, a saturated or unsaturated alkyl group; R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are, independently, hydrogen or a saturated or unsaturated C.sub.1-100 alkyl group; m is an integer of 1 to 6; and p and q are, independently, an integer of 0 to 4, and a catalyst component (B) containing an organic aluminum compound having formula (2): ##STR2## where 1, is an integer of 2 to 100, R.sup.5 is a C.sub.1-6 alkyl group, and/or an organic aluminum compound having formula (3) ##STR3## where 1' is an integer of 2 to 100, and R.sup.5 is a C.sub.1-6 alkyl group.

Abstract: A catalyst system for codimerization of alpha-monoolefins and conjugated diolefins to yield 1,4-dienes. The catalyst system includes at least one ruthenium salt and at least one aluminum halide. Suitable aluminum halides include both alkyl aluminum halides and nonalkylated aluminum halides, as well as mixtures thereof.