Perceptual linear prediction (PLP) is widely used in speech recognition systems as a feature extraction method. Also code-Exited Linear Prediction Coder CELP) is one of the well known speech coders which widely used in communication systems. In this paper the application of PLP in speech coding has been discussed. In the first stage the parameters of formant synthesis filter are determined by applying PLP algorithms. Then these parameters are used in coder, code-exited linear prediction coder, to improve the efficiency of this kind of coder. The experiments show promising result in some cases.