Abstract: Designing and preparing flexible thermally conductive materials is important for thermal management of flexible electronic devices. Based on exfoliated aramid nanofiber and aluminum nitride (AlN) nanoparticle, flexible and thermally conductive composite films were fabricated by a sol-gel-film transformation approach. In the composite films, aramid nanofibers forms three-dimensional connective network for providing mechanical support. AlN nanoparticles are filled in the network of aramid nanofiber to impart the composite films with good thermal conduction performance. As a result, the tensile strength and strain at break are 65.5 MPa and 12%, respectively. After folding for 300 cycles, the composite films retain more than 90% of original tensile strength and strain at break. The thermal conductivity is up to 13.98 W·(m·K)⁻¹. Moreover, the composite films show good electrically insulating property and thermal stability. The volume electrical resistivity and initial thermal decomposition temperature are 1.85×10¹⁵ Ω·cm and 524℃. Finally, we demonstrate that the high-performance AlN/aramid nanofiber composite films can be act as flexible substrate for cooling electronics.