Abstract: Dispersibility of cellulose nanocrystal (CNC) in water before and after adding a dodecyl trimethyl ammonium chloride (DTAC) surfactant was investigated, and then polylactic acid (PLA)/CNC composites were prepared by a solution casting method. The results indicated that the aggregation of CNC was effectively reduced with the aid of DTAC, and the compatibility between PLA and surface-treated CNC was improved due to the formation of hydrogen bonding. Moreover, the heterogeneous nucleation of PLA could be promoted in the presence of surface-treated CNC, leading to an increase in crystallinity of PLA matrix. The tensile strength of composites was improved by 70.7 % with the addition of 2 wt % surface-treated CNC, but their elongation at break decreased.