The interaction of the regulatory biologically active peptide Glu-Asp-Arg (EDR) with DNA is considered by spectral, NMR, viscosimetry, and molecular dynamics methods. It was shown that EDR can partly penetrate into the major groove of DNA and affect the base atoms, mainly the N7 and O6 of guanine. It was observed that Mg2+ ions can promote DNA-EDR interaction due to their effective screening of the negatively charged phosphate groups of DNA. This action of Mg2+ remains in salted solution as well.