Design of sustainable bioplastics can be achieved by preparing composites from renewable materials like microcrystalline cellulose (MCC) fibre and biopolymer such as polylactic acid (PLA). The key driving factor that affects their performance is the quality of dispersion of MCC in the PLA matrix. In this study, surface modification, one way to facilitate improved dispersion, is carried out by acetyl chloride. PLA composites were prepared with the acetylated MCC applying solvent casting technique. Confirmation of acetylated group is accompanied by FTIR and NMR study. Change in crystalline property and thermal behaviour is observed by XRD study. Improvement in storage modulus (G') is reflected in shear rheological tests, reaching an optimal value at 2.5 wt%. This improvement is primarily attributed to a more homogeneous dispersion of MCC in the matrix. Rheological percolation threshold is calculated to quantify the level of dispersion. This study is aimed to quantify the level of dispersion of acetylated MCC, as compared to pure MCC by shear rheology. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.