This study investigates the chemical decomposition of periwinkle shell reinforced polyester composite to assess its residue and its possibilities of being recycled. 6M and 8M Nitric acid were added to the composite samples, and the decomposition was monitored by weight reduction. Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Gas Chromatography -Mass Spectrometry (GC-MS) were used to characterize the composite samples and residue. FTIR of the residue showed the appearance and increase of carbonyl and hydroxyl groups, which indicates that bonds were broken, oxidized, and new functional groups were formed. XRD analysis showed a shift in the major diffraction peak from 21.68° to 25.86° 2θ, with crystallinity increasing from 45.36% to 50.72%, confirming structural reordering and formation of new crystalline phases. GC–MS detected aromatic, ester, and aliphatic fragments. This suggests partial depolymerization and oxidation of the resin matrix. The results indicate that nitric acid is a good hydrolysis and oxidative scission agent in degrading the composite. The work sheds light on recycling possibilities for thermoset composites and advances efforts toward sustainable polymer waste management.