We developed a new method of fabricating a divalent copper ion (Cu²⁺) modified DNA thin film on a glass substrate and studied its magnetic properties. We evaluated the coercive field (H_c), remanent magnetization (M_r), susceptibility (χ) and thermal variation of magnetization with varying Cu²⁺ concentrations [Cu²⁺] resulting in DNA thin films. Although thickness of the two dimensional DNA thin film with Cu²⁺ in dry state was extremely thin (0.6 nm), significant ferromagnetic signals were observed at room temperature. The DNA thin films with a [Cu²⁺] near 5 mM showed the distinct S-shape hysteresis with appreciable high H_c, M_r and χ at low field (≤600 Oe). These were primarily caused by the presence of small magnetic dipoles of Cu²⁺ coordination on the DNA molecule, through unpaired d electrons interacting with their nearest neighbors and the inter-exchange energy in the magnetic dipoles making other neighboring dipoles oriented in the same direction.