Light emitting diode (LED) has been largely used in industry of consumer electronics such as cell-phones, PDAs, and computers. Since all light sources convert electric power into radiant energy and heat, LED also does the same with an increase of its power. Generally, it only converts 15~25% of electric power into visible light; the rest of the power, 75~85%, is converted into heat. This excess heat should be conducted away from the LED die to circuit boards or heat sinks since heat affects directly performance of the LED. The piled heat in LED products brings color shift and reduces light output very rapidly. Furthermore, the lifecycle of LED products shorten if the heat problem continues. In order to prevent LED products from these negative effects, effective thermal resistance paths need to be achieved so that LED products let the heat conduct from the LED to the outside such as printed circuit board. In this research, optimization studies on thermal-via is to be performed. The 1W and 3W LED assembled printed circuit board with 16 different via designs is set up to measure its temperature for 4 hours in a real time. It was obtained by this work that the optimized thermal via was very effective to dissipate the heat from the LED.