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With the miniaturization, high frequency of electronic devices, and low‐carbon and sustainable development, higher requirements are put forward for thermal conductive polyurethane composites in terms of comprehensive performance and renewable raw materials. Herein, choosing bio‐based polyurethane (PU) derived from castor oil as matrix, and liquid metal (LM) and aluminum hydroxide (ATH) as hybrid thermal conductive filler, castor oil‐based PU composites were developed via high‐speed rotation and in‐situ polymerization method. The LM‐ATH hybrid filler displayed a synergistic enhancement effect on the thermal conductivity of composites due to the presence of LM‐bridging significantly improved the effective contact probability between ATH fillers. The thermal conductivity of 50LM‐ATH/PU reached 1.69 Wm−1 K−1, which was 9.9 times and 1.4 times higher than that of pure PU and 50ATH/PU, respectively. Notably, the 50LM‐ATH/PU exhibited outstanding mechanical properties including tensile strength up to 4.0 MPa and adhesion strength up to 7.9 MPa, especially elongation at break up to 120% which was improved by 200% compared with 50ATH/PU (40%). Additionally, the composite possessed excellent electric insulation, thermal stability, and inflaming retarding properties, showing great application potential in the electronic devices field. Highlights: Castor oil‐based PU composites with ATH‐LM hybrid filer were developed.LM‐ATH hybrid filler of 2:8 promoted the thermal conductivity of composites.Hybrid filler than ATH‐endowed composites with better mechanical properties.The ATH‐LM/PU exhibited excellent electric insulation. [ABSTRACT FROM AUTHOR]