The aim of this article is to study the influence of physical treatment on morphology, wettability, fine structure of fibers and its impact on the interfacial adhesion of natural fiber-reinforced thermosets. For that purpose, jute fibers were treated with argon cold plasma for 5, 10, and 15 min and processed for composite with unsaturated polyester resin. Scanning electron microscopy (SEM) micrograph had shown the rough surface morphology and degradation of fiber due to etching mechanism causes by plasma. Surface properties of fibers before and after treatment were determined by mean of contact angle determination and fine structural details by Fourier transform infrared-spectroscopy (FT-IR). Plasma treatment resulted in the development of hydrophobicity in fibers, that is contact angle were found increasing with water. This could be due to the decrease in phenolic and secondary alcoholic groups or oxidation of basic structural component, lignin and hemicelluloses after plasma treatment as studied by FTIR. Rough surface morphology and development of hydrophobicity of fiber after plasma treatment resulted in the better fiber/matrix adhesion as revealed from SEM micrograph of plasma treated fiber composite. However, among all treated fiber composite, flexural strength of composite prepared with 10 min plasma treated fiber only had shown improve mechanical strength of ~14% in compare to raw fiber composite.