Polylactide (PLA)/Acetylated cellulose nanocrystal (ACN)/SiO2 composite was prepared by solution casting and processed by compression molding. ACN was synthesized by surface modification of cellulose nanocrystal and neat PLA was prepared as a reference sample. The content of ACN and SiO2 were 0.5 wt% and 1, 3, and 5 wt%, respectively. ACN was used as reinforcement of polymer matrix and SiO2 was supposed to play a role as nucleation agent to increase crystallization rate of PLA/ACN/SiO2 composite. FT-IR was employed to confirm that acetyl group was substituted to the cellulose nanocrystal surface. Non-isothermal crystallization behavior was performed with the cooling rate of 2.5, 5, 10, or 15oC/min. Avrami equation and Ozawa equation showed deviations while interpreting the non-isothermal crystallization behavior of the composite. On the other hand, Avrami-Ozawa equation seemed to perform perfect prediction. Activation energy of growing crystals was calculated by Kissinger’s equation and Takhor’s. As SiO2 content increases, the activation energy decreases due to the nucleating effect. Spherulite growth behavior was observed by polarizing optical microscope and spherulite growth rate, the number of spherulite versus crystallization time have investigated. WAXD demonstrated that crystallinity of the composite increase with the increase content of SiO2. Increased thermal stability of the composites was observed with the increased loading level of SiO2. Mechanical properties of the composites were investigated and the PLA/ACN/SiO2 composite had higher tensile strength and tensile modulus than neat PLA, indicating ACN act as reinforcement. The PLA/ACN/SiO2 composite can be used to reduce processing cost and can be applied to non-toxic products such as foodstuffs, toys, and housewares. This research was supported by the National Research Foundation of Korea (Project No. 2013-022313). Keywords: poly(lactide), cellulose nanocrystal, Silica, Non-isothermal crystallization