The paper presents a novel method for demodulating the binary phase shift keying (BPSK) signals basing on adaptive filtering. The commonly used least mean square (LMS) error adaptive filtering algorithm is employed for studying the demodulating procedure and the performance of the novel adaptive BPSK demodulation. The novel adaptive BPSK demodulation does not need the adaptive filter completing convergence. The performance of the method in theory is compared with computer simulating results. It shows that the error rates in simulation agree well with that in theory. Also, it is indicated that the demodulation method has many advantages over conventional ones, such as the powerful anti-noise ability, the small transfer delay, and the convenient implementation with DSP technology, and has lower error rates than correlation modulation at the same sample rate.