On May 25, 2009 North Korea executed a second nuclear test in the vicinity of P'unggyeri where the first nuclear test was performed on October 9, 2006. Seismic signals from the two underground nuclear explosions (UNEs) are recorded at broadband stations in South Korea and China. Seismic signals from fourteen broadband stations operated by the Korea Institute of Geoscience and Mineral Resources (KIGAM), three broadband stations of Korea Meteorological Administration (KMA) in South Korea and the Mudanjiang station (MDJ) of GSN in China are used for this study. Clear P_n, P_g, and L_g phases propagated over 800 km. The nearly co-located two UNEs and seismic recordings at the same stations enable us to estimate the ratio of the P_n and P_g displacement amplitude spectra between two events by eliminating the path effect. The 95% confidence interval of the mean yield ratio is constrained as a function of the depth ratio and all the estimates of P_n and P_g spectral ratios. The mean yield ratio ranges from 3.45 to 6.36 in the 95% confidence interval based on the depth range estimates by Bennett (2008, 2009).