Measurements of the temperature distributions of the cooling air flow inside a computer system have been made. An investigation of the optimum cooling condition for the computer system has also been made. Seventy-one K-type (Chromega-Alumega) thermocouples were used to measure distributions of the air flow temperature inside the computer system. They were calibrated against the standard platinum resistance thermometer (PRT) in a constant water circulating bath within an accuracy of ${pm}0.15^{circ}C$. It was found that the number and position of cooling fans as well as their operating condition, whether air intake or air discharge, can greatly influence the cooling effectiveness in the computer system. The results show that the flow rate of intake air should not be higher than that of the discharge air for the most effective cooling. It follows that the optimum cooling has been achieved inside the computer when the three fans are positioned in the inlet front, outlet back, and outlet top in the computer, respectively. Under these conditions, not only is the average temperature inside the computer system maintained at an appropriate level, but the most effective cooling around the central processor (CPU) and graphic card which are responsible for the largest amount of heat dissipation can be accomplished.