A reasonably developed measurement uncertainty analysis approach of a sodium-to-air heat exchanger performance test was conducted for quantified error evaluation. A heat transfer rate of sodium-to-air heat exchanger was calculated temperature and flow rate measured with instruments having some of errors. These error components could affect to the total heat transfer rate obtained the experiment, and it is very essential to determine the quantity of total error in the experiment and measuring system. Total error quantity of our heat transfer rate in the experiment was obtained through the conservative view point and reasonable procedure of measurement uncertainty analysis including the reasonable determination of error components and the error propagation to other parameters for calculation. After the determination of error components, we estimated the bias error and the precision error quantities, separately. As a result, the error quantity in the sodium-side and air-side shows -5.69 %~+3.90 % and ±10.58 %, respectively. The developed methodology for measurement uncertainty analysis can be adapted for other heat exchanger systems, and it can support to estimate error quantities of heat transfer rate in experiments.