Abstract: To address the growing demand for thermal interface materials (TIMs) with superior thermal conductivity and mechanical performance in modern electronic devices, composite films incorporating high filler contents have emerged as promising candidates. However, limited research has been conducted on composite films with filler contents exceeding 50wt% that simultaneously satisfy both mechanical and thermal requirements, primarily due to fabrication cost constraints and experimental complexities. In this study, high-content hexagonal boron nitride (hBN) nanosheets/poly(vinyl alcohol) (PVA) composite films were synthesized via a facile template-assisted method combined with ultrasonication-assisted liquid-phase exfoliation, achieving a maximum filler content of 80wt%. Systematic investigations of their mechanical properties and anisotropic thermal conductivities (in-plane and out-of-plane) revealed that these composite films exhibit exceptional modulus (4-5 GPa) and high thermal conductivities (in-plane: 12-15 W·m⁻¹·K⁻¹; out-of-plane: 1.2-1.8 W·m⁻¹·K⁻¹) at ultrahigh filler contents. These synergistic properties position the developed films as competitive candidates for advanced TIMs applications.