Abstract A charge transfer complex of o-phenylenediamine (OPD) as donor with 3,5-dinitrosalicylic acid (DNSH) as acceptor, was synthesized and characterized by FTIR, 1H NMR, 13C NMR, mass spectroscopy, elemental analysis and X-ray crystallography. The structural investigations exhibit that the cation and anion are joined together by strong N+H⋯O− type hydrogen bonds and stoichiometry of CT complex was found to be 1:1. The CT (charge transfer) complex shows remarkable interaction with Calf thymus DNA, and the CT complex was also screened for its microbial activity such as antimicrobial and antifungal activities. A molecular frame work through H-bonding interactions via n→π* transitions between neighboring moieties is found which is responsible for high melting point of resulting CT complex. This has been attributed to the formation of 1:1 CT complex.