The recent findings from the study on binding of small molecules with DNA duplex suggested that the intercalation of a tricyclic heteroaromatic molecule, Department of Physics, Integral University, Kursi Road, Lucknow-226026, IndiaDepartment of Physics, Integral University, Kursi Road, Lucknow-226026, India, with natural double stranded DNA provided thermal stabilization to the complex. In this study, we reported theoretical analysis of thionine binding with herring testes DNA (Type XIV, 41mol%GC) by using an amended Zimmand Bragg theory, to reveal the melting behaviour and heat capacity of herring testes DNA with and without thionine binding. We used experimental models of Paul et al. (2010) for the study. The sharpness of transition has been examined in terms of half width and sensitivity parameter (ÂH/ó). The results of theoretical analysis concluded that the various parameters such as heat capacity curve, transition profile, half widths and sharpness of the transition are in good harmony with the experimental measurements for interaction of thionine. Accordingly, the theoretical analysis proposed in this study may be useful to understand interaction of small molecules with DNA. This approach may also be applied to design DNA binding therapeutic molecules and in drug innovation.