The　flow　boiling　characteristics　of　CO2/R152a　zeotropic　mixtures　with　three　mass　fractions　(22.1/77.9,　47.4/　52.6　and　65.3/34.7　wt.%)　and　the　pure　components　in　a　2　mm　horizontal　tube　are　experimentally　studied.　The　flow　boiling　characteristics　are　tested　in　the　range　of　temperature　glide　of　30.9-38.3　degrees　C,　mass　flux　of　200-400　kg/m2s,　heat　flux　of　12-36　kW/m2,　and　saturation　temperature　of　5-15　degrees　C.　Flow　patterns　are　observed　and　the　flow　pattern　map　is　also　described,　and　the　heat　transfer　and　pressure　drop　characteristics　of　working　fluid　are　also　conducted.　Furthermore,　a　new　correlation　to　predict　the　heat　transfer　coefficient　of　large　temperature　glide　working　fluid　is　proposed.　The　results　show　7　types　of　flow　patterns　are　recorded,　showing　the　flowing　char-acteristic　between　the　conventional　and　microscale　channel.　The　heat　transfer　coefficient　of　CO2/R152a　in-creases　slowly　with　vapor　quality,　and　decrease　rapidly　when　vapor　quality　reaches　to　the　initial　dryout　vapor　quality,　which　is　lower　than　that　of　pure　CO2.　The　mass　transfer　resistance　and　sensible　heat　resistance　shows　a　severe　deterioration　effect　on　the　flow　boiling　heat　transfer　due　to　the　high　temperature　glide　as　the　sensible　heat　accounts　for　13.12-15.44　%　for　the　mixture　CO2/R152a.　The　frictional　pressure　drop　gradient　of　CO2/R152a　increases　with　mass　flux,　and　decreases　with　the　increase　of　saturation　temperature　and　mass　fraction　of　CO2.　Considering　the　mass　transfer　resistance　and　effects　of　non-negligible　sensible　heat　contribution,　a　new　heat　transfer　correlation　is　proposed,　with　the　mean　absolute　deviation　of　16.9　%,　which　shows　an　acceptable　pre-diction　accuracy　compared　with　the　reported　data　in　the　literatures.