ST segment is the most important diagnostic parameter to finding myocardial ischemia. Generally physicians make theirs effort to find the change of ST level and shape in ECG to diagnose myocardial ischemia. Most of algorithms that have been developed until now place importance on the ST segment depression and elevation. However, ST change in shape is also good parameter to find a heart disease and it should be considered prudently. The aim of this study is to detect the change of ST in shape using a polynomial approximation method. The developed algorithm finds the least squares curve for the data between S wave and T wave in ECG and calculates the variance of ST shape. An approximate curve of ST is represented by one polynomial over the whole ST or three polynomials for the segmented ST by three parts. The algorithm considers only the relative change of ST shape based on the reference ST, normal shape typically. From the results of the developed algorithm, we can acquire visually the information about the place to include the change of ST shape in the test ECG provided by European ST database.