Degradation of mRNA by RNA interference is one of the most powerful and specific mechanism for gene silencing. Owing to this property, siRNAs are emerging as promising therapeutic agents for the treatment of inherited and acquired diseases, as well as research tools for the elucidation of gene function in both health and disease. Here we have explored the potential of polyethylenimine (PEI) to deliver siRNA to mammalian cells. Nanoparticles of PEI were prepared by acylating PEI with propionic anhydride followed by cross-linking with polyethylene glycol-bis(phosphate). The nanoparticles size as revealed by DLS studies was found to be approximately 110 nm and AFM investigations showed spherical and compact complexes with an average size of 100 nm. For electro-neutralization of negative charge of siRNA higher amount of nanoparticles was required as compared to native PEI. The siRNA delivery efficiency of nanoparticles was assessed by using siRNA against gene coding for green fluorescent protein (GFP). The gene silencing efficiency of PEI nanoparticles was found to be comparable to commercially available transfecting agent Lipofectin but with reduced cytotoxicity.