Nanosized calcium carbonate (nano-CaCO3)-filled poly-L-lactide (PLLA) biocomposites were compounded by using a twin-screw extruder. The melt flow behavior of the composites, including their entry pressure drop, melt shear flow curves, and melt shear viscosity were measured through a capillary rheometer operated at a temperature range of 170200 degrees C and shear rates of 50103 s-1. The entry pressure drop showed a nonlinear increase with increasing shear stress and reached a minimum for the filler weight fraction of 2% owing to the bearing effect of the nanometer particles in the polymer matrix melt. The melt shear flow roughly followed the power law, while the effect of temperature on the melt shear viscosity was estimated by using the Arrhenius equation. Hence, adding a small amount of nano-CaCO3 into the PLLA could improve the melt flow behavior of the composite. POLYM. ENG. SCI., 52:18391844, 2012. (c) 2012 Society of Plastics Engineers