A VFR LPC vocoder using optimal interpolation is presented in this paper. In the encoder, some representative frames of an utterance are selected for transmission. In the decoder, LPC parameters of all untransmitted frames are restored by optimal interpolation. Simulation results show that this coding scheme outperforms the conventional VFR vocoder using linear interpolation. By incorporating contour quantization of gain and pitch information, a low variable-rate LPC vocoder is realized. An informal listening test shows that very high intelligible reconstructed speech was obtained at an average data rate of 300 bps.