This research endeavor explores the effect of economical and environment‐friendly treatment of sisal fibers, prior to their incorporation into poly‐lactic acid (PLA). Biocomposites incorporating sisal fibers (30% [w:w]) treated with sodium bicarbonate (10% [w:v]) aqueous solution for varying time periods (24, 72, 120, and 168 h) were developed using extrusion‐injection molding process. Thermogravimetric analysis, morphological examination, Fourier‐transform infrared spectroscopy, and lignocellulosic composition analysis of raw and treated sisal fibers established a gradual removal of hemicellulosic content from fiber surface with increasing treatment time. Biocomposites incorporating sisal fibers treated for 72 h exhibited optimum tensile, flexural, and compressive properties. While in case of impact testing, biocomposites incorporating sisal fibers treated for 24 h exhibited maximum impact strength. The optimum results were found comparable to sodium hydroxide treated sisal fiber‐reinforced biocomposites. Hence, considering commercialization of biocomposites, sodium bicarbonate treatment offers huge potential to substitute ecologically hazardous sodium hydroxide treatment ensuring good mechanical properties. POLYM. COMPOS., 39:4310–4321, 2018. © 2017 Society of Plastics Engineers