We present propagation characteristics of the short-period seismic phases Sn and Lg in northeastern China and Mongolia. Three-component broadband and short-period seismograms from the Global Seismic Network station ULN and the Chinese Digital Seismic Network stations BJT, HIA, and MDJ were used in this study. The digital waveforms were bandpass filtered (1.0–5.0 Hz) and were used to rank Sn and Lg amplitudes relative to the Pn and Pg phases. The short-period Sn waveforms exhibit great variability. Efficient Sn propagation is observed in southern Siberia and along the Daxinganling Mountains. Inefficient Sn transmission is found near Lake Baikal and most of northeastern China. Sn does not propagate across Mongolia or the North China Plain. In northeast China, zones of attenuation exist within regions of extension and high heat flow. In Mongolia, severe Sn attenuation suggests the presence of a partially melted uppermost mantle. The zones of inefficient Sn propagation coincide with zones of low Pn velocities (∼7.9 km/sec) determined by Wu et al. (1998). In contrast, the Lg seismic phase has large amplitudes and propagates efficiently for all distances in northeastern China and Mongolia.