The nanometer calcium carbonate (nano-CaCO3)-filled poly-L-lactide (PLLA) biocomposites were prepared using a twin-screw extruder. The first normal stress difference of the composites were measured by means of a capillary rheometer under experimental conditions with temperatures ranging from 170 to 200 degrees C and shear rates varying from 50 to 10(3) s(-1). The first normal stress difference (N-1) increased roughly linearly with increasing shear stress ((w)). The sensitivity of the N-1 to (w) increased with an increase of the die length--diameter ratio, and the N-1 value varied slightly with the filler weight fraction (phi(f)) as test temperature was constant. When the shear stress was fixed, the N-1 reached a minimum value for phi(f) = 1%. The values of the N-1 of the composite melts decreased roughly linearly with a rise of temperature when the shear rate was constant. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers