Swift Heavy Ion (SHI) irradiation induces chemical and structural changes in polymers by evolving various gases and gaseous fragments. The evolution of gases as a result of chain scissoring and bond breaking leads to cross-linking and cluster formation. Study of the evolved gases helps in understanding the various chemical and structural changes occurring within the polymer under the effect of SHI irradiation. In the present work, Poly (o-toluidine) (PoT), a derivative of polyaniline, is prepared by chemical oxidation polymerization and is blended with polyvinylchloride (PVC) to achieve self supported films. These PoT-PVC blend films were irradiated by 60 MeV Si 5+ ions at different fluences and evolved gases were monitored on-line by Residual Gas Analyzer (RGA). Pre and post irradiation FTIR, UV-Visible absorption and XRD studies have been carried out on these films to observe the changes in chemical/structural and optical properties. An effort has been made to correlate the evolved gases and structural properties after irradiation.Copyright © 2011 VBRI press.