ABSTRACT In the present work, ladies finger (LF) fiber has been utilized as reinforcement in thermoplastic polymer, polyethylene terephthalate (PET). The extracted fibers were chemically treated, and the effect of chemical treatment of fibers on mechanical and thermal properties of composites was investigated and discussed. For this purpose, the fibers were treated with chemicals like sodium hydroxide at various concentrations (2%, 3%, 4%, and 5%). Then, the chemically treated fibers with varying weight percentage (0, 10, 20, 30, and 40 wt%) were reinforced in PET to develop new composites, and its various properties like mechanical properties, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray diffraction were thoroughly investigated and compared with untreated fiber composites and neat PET. It has been observed that the composites fabricated with treated LF fibers reveal improved properties as compared to composites containing untreated fibers. Moreover, a better fiber–matrix bonding is also observed in scanning electron microscopy images. Twentywt% of fiber loading reveals highest mechanical properties as compared to other fabricated composites and can be suitable for packaging applications.