The catalyst formation by reacting magnesium diethoxide with titanium tetrachloride in the presence of stereoregulating electron donor - di-n-butylphthalate (DBP) - is studied by sampling the intermediate products during catalyst synthesis. Chemical and phase composition, porous structure, activity and stereospecificity of these products are investigated. It is show that before DBP adding the X-ray amorphous product consisting of MgCl2 and TiCl3(OEt) is formed. This product has micro-mesoporous structure, very high surface area, but low activity and low stereospecificity. DBP has a significant effect on both the chemical composition of the catalyst due to removing inactive TiCl3(OEt), entering DBP and TiCl4 in solid product and formation of MgCl2 crystallites with mesoporous structure. At the same time the significant increase of the activity and stereospecificity is observed. Following TiCl4/chlorobenzene treatment of solid product completes these processes, provides some increasing the surface area at similar mesoporous structure and additionally increases activity and stereospecificity. (C) 2013 Elsevier B.V. All rights reserved.