Polylactic acid (PLA) is one of the most attractive biodegradable polymer due to various attractive properties including high modulus, clarity, and its cost has been becoming economically reasonable. However, the brittleness of PLA remains an important drawback that limits its utilization in some applications. In this work, we focus on improving the mechanical properties of PLA, specifically elongation at break, by mean of incorporations of different natural fibers to PLA to fabricate 100% fully biocomposites. Three natural fibers were compared including bamboo leave, sugar crane, and coir fibers. An alkaline treatment of the fibers was carried out to compare its effects on improving mechanical properties. Compounds of PLA and a constant content of 5 wt% fibers, both treated and untreated, were prepared using twin screw extruder, followed by palletization. Compression molding was used to prepare the composite sheets. Tensile test results showed increases in moduli of the 5 wt% fiber/PLA composites raking from bamboo leave fiber >coir fiber> Neat PLA>sugar crane fiber. Similar trend was observed for their tensile strength. For elongation at break, significant improvement of 19 and 16 folds were found in the composite containing bamboo leave and coir fibers, respectively. Using scanning electron microscope (SEM), it was found that the alkaline treatment increased fiber surface roughness which provided better mechanical interlocking between the treated fibers and PLA matrix. Therefore improved moduli and tensile strength were observed in all fibers. On the other hand elongation at break suffered from the fiber treatment.