This paper deals with the problem of using the Describing Function (DF) technique, in the analysis of practical control systems which contain more than one nonlinear element in the control loop. The DF technique is analysed to investigate its limitation in nonlinear system design. Both single input-single output and multiple input-single output systems are considered. Computer simulation is utilized to check results. It has been shown that this technique can be used in control systems which contain only one nonlinearity and with single input applications. However, in the case of systems which have more than one nonlinearity in the control loop, it is shown that: the DF Is not an accurate method of analysis specially in the multiple input applications.