Al₂O₃powder with various particle sizes was prepared by milling process and mixed together with epoxy resin in order to increase the thermal conductivity of resin and decrease the junction temperature of the LEDs. Al₂O₃ powder filled epoxy resin was applied as thermal interface material (TIM) for an effective system level analysis of thermal transient measurement. The result depicted that the milled Al₂O₃ powder for 3 hour powder showed the highest thermal conductivity and hence lower in thermal resistance of LED. Moreover, the driving currents also influence the thermal resistance and achieved low thermal resistance when measured at 350mA. The thermal properties of the sample were tested using t3ster. The surface morphology of the samples was tested using FESEM.