Considering　the　issues　of　energy　saving　and　environment　protection,　the　performance　of　refrigeration　systems　requires　to　be　improved.　In　recent　years,　nano-fluids　have　attracted　greatly　attention　from　the　researchers　due　to　their　outstanding　thermal　characteristics.　In　this　work,　the　published　investigations　on　the　preparation　and　characterization　of　nano-fluids　have　been　discussed　at　first.　Furthermore,　the　key　thermo-physical　properties　of　nano-fluids,　such　as　thermal　conductivity,　viscosity,　specific　heat　and　density　have　been　summarized.　Finally,　the　performance　enhancements　in　different　types　of　refrigeration　systems　by　using　nano-fluids　have　been　reviewed.　It　is　concluded　that　nano-fluids　as　refrigerant,　lubricant　or　secondary　fluid　have　wide　potential　application　in　refrigeration　systems.