Environmentally-friendly　polymers　which　can　be　recycled　and　reused　at　the　end　of　life　are　urgently　needed　for　the　development　of　advanced　high-voltage　direct　current　(HVDC)　systems.　Polymer　nanocomposites　have　attracted　considerable　attention　owing　to　their　unique　features　arising　from　synergistic　combination　of　inorganic　fillers　and　polymer　matrices.　Here　we　describe　thermoplastic　poly(ether　imide)　(PEI)　nanocomposites　that　contain　boron　nitride　nanosheets　(BNNSs).　It　is　found　that　the　polymer　nanocomposites　exhibit　simultaneous　improvements　in　multiple　physical　properties,　such　as　the　DC　electrical　breakdown　strength,　volume　resistivity,　mechanical　strength　and　thermal　stability,　along　with　substantial　reduction　in　loss　tangent,　compared　with　neat　PEI.　A　great　improvement　in　thermal　conductivity　has　been　attributed　to　the　presence　of　BNNSs　in　the　composites,　which　improves　heat　dissipation　in　comparison　with　neat　polymers.　The　composite　approach　provides　a　promising　solution　for　alleviating　temperature-gradient　distribution　and　addressing　heat　accumulation　issues　in　HVDC　equipment,　and　enables　broader　applications　of　insulation　materials　in　HVDC　systems　operated　under　high　voltages.　©　2019　IEEE.