Next-generation insulating materials must operate reliably under high-temperature and high-voltage conditions while maintaining excellent thermal, electrical, and mechanical properties. In this study, m-aramid short fibers were blended with poly(amic acid) (PAA) at various ratios to prepare m-aramid/PI composite films via stepwise thermal imidization. The fibers and PAA were dissolved in N,N-dimethylacetamide containing lithium chloride, cast into films, and subjected to multi-step thermal treatment to achieve complete imidization. This work investigates the relationship between m-aramid fiber content and thermal imidization conditions on the structural, thermal, and electrical properties of the resulting composites. The findings are expected to elucidate how fiber reinforcement enhances thermal stability, dielectric strength, and mechanical performance, thereby validating m-aramid/PI composites as promising candidates for high-performance insulating applications.