In video coding systems, an effective rate control method is one of the most important issues for the good video quality. This paper presents an adaptive rate control scheme based on buffer fullness, quantization, and buffer utilization for very low bit rate communication lines, such as 16kbit/s, 32kbit/s, and so on. The strategy is implemented on H.263, which is a video coding algorithm for narrow band telecommunication channels up to 64kbit/s recommended by ITU-T SG15, to show the effectiveness. The simulation result shows that the suggested rate control scheme has better SNR performance and buffer utilization of source coder than those of linear and non-linear[11] buffer control strategies.