Investigating the compatibility mechanism of hybrid composites based on two polymers and one mineral nanofiller is a challenge that needs to be better understood. This study evaluates the effect of calcium carbonate (nCaCO(3)) nanoparticles as co-compatibilizers in a blend based on poly(lactic acid) (PLA), polyethylene from renewable sources (HDPE) and maleic anhydride grafting polyethylene (HDPE-g-MA or MA) using rheological and morphological analyses. Morphological assessment by scanning electron microscopy showed the formation of co-continuous-like phase morphology when nCaCO(3) was added to the PLA/MA/HDPE blend, indicating that nCaCO(3) affected the dispersion of PLA domains in the HDPE matrix. Rheological characterization carried out by stress relaxation and sweep frequency response analysis demonstrated that the addition of nCaCO(3) improved the solid-like behavior of the blend, corroborating the morphological results. Additionally, an interaction mechanism of nCaCO(3) as a co-compatibilizer was also proposed.