Nanodielectrics,　which　are　concentrated　in　polymer　matrix　incorporating　nanofillers,　have　received　considerable　attention　due　to　their　potential　benefits　as　dielectrics.　In　this　paper,　short-term　breakdown　and　long-term　failure　properties　of　nanodielectrics　have　been　reviewed.　The　characteristics　of　polymer　matrix,　types　of　nanoparticle　and　its　content,　and　waveforms　of　the　applied　voltage　are　fully　evaluated.　In　order　to　effectively　comment　on　the　published　experimental　data,　a　ratio　k　has　been　proposed　to　compare　the　electric　properties　of　the　nanodielectrics　with　the　matrix　and　assess　the　effect　for　nanoparticles　doping.　There　is　evidence　that　the　short-term　breakdown　properties　of　nanodielectrics　show　a　strong　dependence　on　the　applied　voltage　waveforms.　The　polarity　and　the　cohesive　energy　density　(CED)　of　polymer　matrix　have　a　dramatic　influence　on　the　properties　of　nanodielectrics.　Nanoparticle　doped　composites　show　a　positive　effect　on　the　long-term　failure　properties,　such　as　ageing　resistance　and　partial　discharge　(PD)　properties　of　nanocomposites　are　superior　than　microcomposites　and　the　matrix.　The　larger　the　dielectric　constant　and　CED　of　the　matrix　become,　the　more　significant　improvements　in　long-term　performance　appear.　Based　on　the　reported　experimental　results,　we　also　present　our　understandings　and　propose　some　suggestions　for　further　work.