MPEG’ylated poly(2-hydroxypropylene imines) were synthesised using 1,3-diamino-2-propanol, 1,3-dibromo-2-propanol and methoxy poly(ethylene glycol) (MPEG, Mn 1000, 2000, 5000). Trying to find conditions favourable for attachment of MPEG chains, MPEG iodide was either added to the initial mixture of the monomers (method A), or was introduced later, at the end of the reaction (method B). MPEG’ylated derivatives of PHPI were characterized by FTIR and NMR spectroscopy, SEC, DLS, DSC and potentiometric titration and were tested for DNA and siRNA delivery in vitro. Efficiency of high MW / low MPEG content PHPI derivatives in DNA transfection was similar to that of PHPI. MPEG grafting had a positive effect on siRNA delivery: high MW polymers with low content of MPEG performed significantly better than non-MPEG’ylated PHPI and low-molecular-weight polymers with high content of MPEG. The length of MPEG chains attached to the polymers had no effect over the transfection efficiency.