Abstract: A combination of a hot/cold wire technique was used for thesimultaneous measurements of instantaneous velocity and temperature in avertical pipe. The detailed study of the effects of buoyancy on flowcharacteristics and heat transfer of opposing mixed convection had beencarried out experimentally. The performance of cold wire for temperaturecompensating the velocity reading of a hot-wire probe due to varying fluidtemperature was assessed. Heat transfer results for opposing mixedconvection have been presented in non-dimensional equations using thebuoyancy parameterΩ(Ω= Grd / Red2), inwhich Red ranges from 900 to 18,000 andΩfrom 0.004899 to0.5047. It is found that theheat transfer is enhanced due to buoyancy effect. With the increasing ofGrd (Grashof number), the temperature fluctuation, streamwise Reynoldsnormal stress and streamwise heat flux are increased, especially in the nearwall region. The combination of hot/cold wire enables the study ofnon-isothermal flow characteristics, thus it is helpful to look inside ofbuoyancy effects on heat transfer in the mixed convection flows.