This paper presents a new voice activity detection (VAD) method using the Gaussian distribution and a uniformly most powerful (UMP) test. The UMP test is employed to derive the new decision rule based on likelihood ratio test (LRT). This method requires the Rayleigh distribution for the magnitude of the noisy spectral component and the adaptive threshold estimated from the noise statistics. Experimental results show that the proposed VAD algorithm based on UMP test outperforms the conventional scheme.