This paper shows a resonable prediction equation to estimate the nonlinear moment-rotation behavior of semi-rigid beam-to-column connection. The effect of flexible connection to the moment-rotation behavior is shown by the standardization constant K using the experimental data. Prediction model is composed of the modified Menegotto-Pinto power function which is the curve fitting model. This prediction equation is compared with the polinomial prediction model suggested by Frye(1975) and the experimental results reported by Kishi and Chen(1986).