Present study allows us a better understanding of the interaction of nitidine, a benzophenanthridine alkaloid with single stranded polyriboadenylic acid [ss-poly (rA)]. The interaction leads to self-structure induction in ss-poly (rA) under the experimental condition of pH 7.0. Interaction of nitidine with ss-poly (rA) was ascertained by monitoring the change in absorbance, fluorescence intensity and circular dichroism values. Binding mode of nitidine with ss-poly (rA) was observed to be intercalation as confirmed from the quenching and viscometric studies. The association was characterized by both negative enthalpy and entropy changes accompanying with a moderately high binding constant of 5.10×10(5)M(-1). Nitidine induced double helical organization in single stranded poly (rA) under the experimental pH.