The present study aims to determine the current-voltage characteristics (CVCs) of nonlinear elements of an RC circuit as well as its functions which would allow one to approximate the experimental data. For this purpose, the well-known least squares method (LSM) has been used. In order to approximate the CVCs characteristics of elements of nonlinear circuits, which are often used in practice, the following functions have been used as approximating functions: exponential function, hyperbolic sine, and polynomial of the fifth degree. Algorithms and computer programs have been also developed to determine these functions.Algorithms and computer programs for solving problems proposed in this paper can be used for computer analysisof nonlinear radio circuits based on active RCs.