Test compression/decompression is an efficient method for reducing the test application cost. In this paper we propose a response compression method based on Huffman coding. The proposed method guarantees zero-aliasing because faulty responses are mapped into code words, not just fault-free ones. Moreover the method is independent of the fault model and the structure of a circuit-under-test, and uses only the knowledge of the fault-free responses corresponding to a given test input set. Experimental results of the compression ratio and the size of the encoder for the proposed method are presented.