The physico-chemical analysis of terbium caprylate (anionic surfactant) was carried out by FTIR, XRay Diffraction (XRD) and thermogravimetric analysis (TGA) measurements. The IR results have shown that caprylic acid exist as dimer through hydrogen bonding and terbium caprylate possess partial ionic character. The Xray diffraction measurements have been used to calculate the long spacings. Thermogravimetric analysis has shown that this compound is thermally stable up to 480°C. The thermal decomposition reaction found zero ordered kinetic and value of energy of activation was found to be in the region of 3.29 to 7.43k cal mol-1 .