Abstract: This paper studies the effect of the varying load on the transmission characteristics of a two-port network and defines the load insensitivity network as the minimum mismatch network. A fifth order minimum mismatch filter is designed by using of Monte Carlo method. The example shows the transmission characteristic of the designed minimum mismatch filter is better than those of the prototype filters, when load impedance is varying. The results demonstrate the minimum mismatch network exists and it can be realized, when a reasonable choice of technical specifications is given.