Polyimine is a novel functional thermoset material with several attractive functions. Yet the mechanical properties of polyimine-based composites have been rarely investigated. In this work, calcium carbonate (CaCO3), a cheap and commonly used reinforcing material, has been chosen as the reinforcing filler to form composites with polyimine through heat-pressing under mild conditions to mimic natural nacre. Elemental mapping shows that CaCO3 particles are evenly distributed in the continuous network of the polyimine matrix. Then thermal analyses and mechanical measurements of hardness, tensile strength, toughness, bending strength, and impact strength have been conducted to characterize the properties of the resultant polyimine composites. The fracture surfaces of the specimens after tensile testing have also been examined by scanning electron microscopy (SEM). The polyimine composites with CaCO3 particles demonstrate remarkable enhancement on multiple mechanical features, especially on tensile properties. More importantly, the polyimine composites fabricated with 6 wt% of CaCO3 particles show simultaneous increases of tensile strength and toughness, which are 56% (from 35.75 to 55.79 MPa) and 110% (from 112.82 to 236.54 MJ/m 3) respectively in comparison with the polyimine matrix. The work presented herein affords a facile and low-cost approach to enhance the mechanical properties of polyimine material for more practical applications.