The Himalayan mountains and their surroundings are hit by a major earthquake in 100-year or less interval. A study conducted in 2002 revealed that Kathmandu valley of Nepal will suffer a great damage if an M8.0 class earthquake hits the region again. In this study, we conduct an ambient ground vibration survey in the valley, which has a thick lacustrine lake deposit, and analyze the recorded data so as to prepare a seismic damage risk map based on the natural periods of the ground. A portable velocity sensor was used in the survey at 172 locations covering the valley core. Fourier analysis of each recorded dataset yielded natural periods of the surveyed ground points, which were then interpreted in terms of the seismic damage risk map.