A variety of isotactic polystyrene-b-poly(ethylene-co-propylene) diblock copolymers were synthesized directly by using TiCl4/MgCl2/Al(i-Bu)(3) catalyst system modified by rare earth compound of NdClx(OR)(y) which was developed in our laboratory. The influence of temperature, catalyst and cocatalyst concentration, prepolymerization time and monomer feed ratio on the copolymerization were investigated and optimized. After successive extracting the copolymerization products with suitable solvents, the isolated block copolymer (about 20-30 wt.% content in total), which is soluble in boiling butanone or chloroform was characterized in detail by C-13 n.m.r. spectroscopy, gel-permeation chromatography (g.p.c), differential scanning calorimetry (d.s.c), X-ray diffraction, transmission electron micrographs (TEM), etc., which showed that this kind of copolymer containing isotactic polystyrene segments was semi-crystalline diblock copolymer with special microphase separation structure.