PURPOSE: To obtain a stable oil suspension useful as a solid catalyst component for the polymerization of α-olefin easy to handle by forming particles containing a transition metal comps. into an oval spherical shape and making the particle size distribution of them narrow.

CONSTITUTION: Particles containing a transition metal compd. such as TiCl2 are formed so that the shape thereof has an oval spherical shape and the particle diameter distribution thereof becomes below 3 in a ratio Dw/Dn of a wt. average diameter (Dw) and a logarithmic average diameter (Dn) and dispersed in mineral oil or silicone oil to prepare an oil suspension. the particles containing the transition metal compd. is obtained, for example, by the activation treatment of a precursor substance corresponding to TiCl3.(AlRCl2)xCy (wherein R is a 2-6C alkyl, C is an electron donating compd, x≤0.2, 0.009<y<0.20).