Magnetic fluids are the colloidal solutions containing suspended magnetic nanoparticles in carrier fluids. The present work analyzed the heat transfer characteristics of de-ionized water and transformer oil (base fluids) based cobalt manganese ferrite (Co1-xMnxFe2O4 coated with oleic acid synthesized via co-precipitation technique) magnetic fluids in varying magnetic field. Experimental investigations were carried out to analyze the heat transfer property of synthesized magnetic fluids (MNF) in varying magnetic field applied in perpendicular direction to the thermal gradient of magnetic fluids. The experimental results indicate that the magnetic fluids show enhancement in heat transfer rate than carrier fluids in absence of magnetic field and it shows decrement in heat transfer rate in presence of varying magnetic field. Thus, the results reveal that the heat transfer characteristics of cobalt manganese ferrite based magnetic fluids was tunable by controlling the direction and influence of magnetic field strength. This tunable heat transfer property of cobalt manganese ferrite based magnetic fluids could be applicable in heat transport phenomena of transformers and in microelectronic devices.