An olefin polymerization catalyst having an excellent polymerization activity and an olefin polymerization process using the catalyst are disclosed. The olefin polymerization catalyst comprises (A) a transition metal compound represented by, for example, the following formula (I) and optionally (B) at least one compound selected from an organometallic compound, an organoaluminum oxy-compound and a compound which reacts with the transition metal compound (A) to from an ion pair; wherein M is a transition metal atom of Group 3 to Group 11 of the periodic table; m is an integer of 1 to 6; A is -O-, -S-, -Se- or -N(R5)-; D is -C(R 7 )(R 8 )-, -Si(R 9 )(R 10 )- or the like; Z is -R 13 and -R 14 , =C(R 15 )R 16 , =NR 17 or the like; R 1 to R 17 are each H, a hydrocarbon group or the like; n is a number satisfying a valence of M; and X is halogen, a hydrocarbon group or the like.