Abstract: Micro-diamonds were introduced into electrical insulator encapsulation gel to investigate their effect on the thermal conductivity.Microstructure studies by a scanning electron microscope showed that the micro-diamonds could be better dispersed in the matrix.No notable phase separation between the micro-diamonds and electrical insulator encapsulation gel matrix were observed.The thermal conductivities of the composites were measured by the Hot Disk Thermal Constants Analyser.The thermal conductivity k was found to increase with the micro-diamonds filler loading.There was a 29.2% enhancement in thermal conductivities for electrical insulator encapsulation gel with 12.5 wt% micro-diamonds loading,as compared with 0.24W/m^*К for the pure electrical insulator encapsulation gel.