<p>The data on the constants of copolymerization of propylene with ethylene over highly active titanium–magnesium catalysts under conditions when produced a statistical copolymer containing 3–5&#xa0;mol% of ethylene was obtained. Catalysts with different particle size and porous structure, as well as catalysts containing different internal stereoregulating donors phthalate, 1,3-diether and succinate were studied. The constant of copolymerization of propylene with ethylene (<i>r</i>₂ value) was found to increase as the average size of catalyst particles increases from 12 to 25&#xa0;µm. A further increase of particle size to 51&#xa0;µm had virtually no effect on the copolymerization ability of catalyst. At the same time, the pores volume for a catalyst with a particle size of 12–14 microns did not affect the value of <i>r</i>₂. It was revealed that catalyst TMC-S containing an internal donor succinate had a highest copolymerization ability (a lower <i>r</i>₂ value compared to catalysts TMC-P and TMC-D containing stereoregulating donors phthalate and 1,3-diether, respectively). The data on the constants of copolymerization ethylene with propylene (the <i>r</i>₁ value) over titanium–magnesium catalysts TMC-D, TMC-P, and TMC-S had been obtained under conditions when a statistical copolymer containing 6&#xa0;mol% propylene was produced. It was found that under these conditions all the catalysts had close copolymerization abilities: copolymerization constant <i>r</i>₁ is independent of the composition of an internal donor. It was found, the propylene/ethylene copolymers produced over phthalate and succinate catalysts have close wide MWD (in contrast to homopolymer), while the copolymer obtained over diether catalyst has a narrower MWD.</p> Graphical Abstract <p></p>