The pollution due to non-degradable material such as plastics, has led to studies the development of environmental-friendly materials. Because of natural sources-based materials and their biodegradability, polylactid acid (PLA) and ijuk fiber are interesting to be modified as composite. In this study, Alkalinization of ijuk fiber, was aimed to enhance compatibility between ijuk fiber and PLA, in order to improve properties of the biocomposite such as crytallinity and thermal behavior. Characterizations were performed by FTIR to obtain compounds content of the ijuk fiber, DSC and TGA to investigate crytallinity behavior of the composite and FE-SEM to observe morphology of the composites. The experimental showed that alkalinization of the ijuk fiber led to wettability enhancement between the ijuk fiber and the PLA due to annihilating lignin and hemicellulose. This treatment also leads to expose micro-fibril cellulose (MFC) in the ijuk fiber, which enhances affinity of bonding with the PLA and PLA crystallinity in the composite.