<p>This study focused at exploring the feasibility of using calcium carbonate (CaCO₃) as a reinforcing filler and compatibilizer for polylactic acid/maize stalk fiber (PLA/MSF) composites. The effect of CaCO₃ on the flammability, thermal, and rheological properties of the PLA/MSF composite was investigated. The hybrid composites PLA/CaCO₃/MSF were prepared using CaCO₃, and pulverized PLA and MSF. The CaCO₃ composition was kept at 5wt.%, while the MSF was varied from 10 to 20 wt.%. By utilizing various characterization techniques, the surface/structural properties of the hybrid composites were analyzed. The results indicated that incorporating CaCO₃ enhanced the dispersion of fibers in the 85/5/10 PLA/CaCO₃/MSF and 75/5/20 PLA/CaCO₃/MSF composites, irrespective of the fiber content. The hybrid systems demonstrated a reduction in pHRR peaks, ranging from 130 to 148&#xa0;kW/m², in contrast to the observed range of 555 to 697&#xa0;kW/m² for the neat PLA, PLA/MSF, and PLA/CaCO₃ composites. In addition, the hybrid composites recorded lower THR values compared to pure PLA and the binary composites. The 75/5/20 PLA/CaCO₃/MSF exhibited the highest storage modulus, whereas increased complex viscosity and G’’ were observed at higher fiber loading (20 wt.%). Calcium carbonate content raised the degradation temperature of the 95/5 PLA/CaCO₃ composite in comparison to neat PLA. In contrast, higher loading of MSF (20 wt.%) had an opposite effect on the PLA/CaCO₃ composites. The results demonstrate the effectiveness of CaCO₃ as a reinforcing filler and compatibilizer in PLA/maize stalk composites.</p>