The reliability of reactor core design is verified by the comparison of measured data and predicted data, which will improve the safety and the economy in plant operation. This report contains the results of the operational data analysis for nuclear key parameters in Yonggwang-2 Cycle-4. The analyzed nuclear parameters are classified into two categories : reactivity parameters and power distribution parameters. It is verified that the predicted values for these parameters not only coincided well with the measured values but satisfied the safety limits. Through this work, it is turned out that some important points(boron biasing, etc.) may be provided in the nuclear design of the next cycle. (Author).