The present invention provides a process for preparation of a solid titanium catalyst component for use as pro-catalyst for a Ziegler-Natta catalyst system. The solid titanium catalyst component comprises a combination of 15 to 20 wt % of a magnesium moiety, 1.0 to 6.0 wt % of a titanium moiety and 5.0 to 20 wt % of an internal donor, said solid titanium catalyst component has an average particle size in the range of 1 to 100 μm, characterized by a three point particle size distribution of D10 in the range of 1 to 10 μm; D50 in the range of to 25 μm and D90 in the range of 15 to 50 μm. The present invention also provides a 15 Ziegler-Natta catalyst system comprising the solid titanium catalyst component and the method of polymerizing and/or copolymerizing olefins by using the Ziegler-Natta catalyst system.