Chemical modification of the sisal fiber is done through dewaxing. Increment in the degree of crystallinity, crystallite size, and bulk density are observed in case of the dewaxed sisal fiber. The partial removal of wax, hemicellulose, and lignin content is confirmed from the FTIR spectra. Better flexural strength and tensile strength are observed in case of dewaxed sisal fiber-reinforced epoxy composite (DSFREC) in comparison to the raw sisal fiber-reinforced epoxy composite (RSFREC). This may be due to the improvement in the adhesion between the fiber and matrix. Lower values of dielectric constant (epsilon(r)) and dielectric loss (tan delta) are also observed in case of DSFREC. The shifting of MaEuro(max)(3) toward higher frequency side with rise in temperature ascribing a correlation between motions of mobile ions and suggests a spread of relaxation times. Moreover, the structural parameters of the fiber are correlated with the mechanical and electrical properties of the composite.