Polylactide (PLA) and calcium carbonate (CaCO3) were melt blended using a twin-screw extruder. The morphology of PLA/CaCO3 composites was observed by scanning electronic microscopy. The linear and nonlinear shear rheological behaviors of PLA/CaCO3 melts were investigated by an advanced rheology expended system. The results show that the CaCO3 particles are evenly dispersed in the PLA matrix. The incorporation of low CaCO3 content (<20%) causes the reduction of the storage moduli, loss moduli, and dynamic viscosities whereas high CaCO3 content (>30%) leads to the increase of the storage moduli, loss moduli, and dynamic viscosities. The composites with high CaCO3 content show pseudo-solid-like behaviors at low frequency. High CaCO3 content also results in a significant increase of flow activation energy and a dramatic decrease of flow index n, which is in consistent with the more serious shear-thinning tendency of high-filled PLA composites melts. The particular rheological responses might be attributed to the formation and destruction of the percolating network. (C) 2009 wiley Periodicals, Inc. J Appl Polym Sci 114: 1648-1655, 2009