A campaign of microtremor measurements was conducted in summer 2007 for assessing local site effects of seismic strong ground motion in metropolitan Beijing. Using the measurements from over 600 sites with approximately 1―2 km spacing covering the entire area inside Beijing’s 5th Beltway, we present the analysis results in the form of contours of the predominant resonant frequency, the thick- ness of the uppermost soft sediments, and the ground motion amplification factor. The microtremor- derived soft sediment thickness is generally in agreement with previous results based on much sparser borehole data, with the revealing of more short-wavelength undulations, which coincide with major geomorphological and neotectonic expressions in metropolitan Beijing. This study provides additional valuable information to the earthquake-resistant design of civil infrastructures and seismic hazard response in metropolitan Beijing. It also provides a feasible geophysical approaching to explore the 3-D structure beneath metropolitan cities. A campaign of microtremor measurements was conducted in summer 2007 for assessing local site effects of seismic strong ground motion in metropolitan Beijing. Using the measurements from over 600 sites with 1-2 km spacing covering the entire area inside Beijing’s 5th Beltway, we present the analysis results in the form of contours of the predominant resonant frequency, the thick-ness of the uppermost soft sediments, and the ground motion amplification factor. The microtremor- derived soft sediment thickness is generally in agreement with previous results based on much sparser borehole data , with the revealing of more short-wavelength undulations, which coincide with major geomorphological and neotectonic expressions in metropolitan Beijing. This study provides additional valuable information to the earthquake-resistant design of civil infrastructures and seismic hazard response in metropolitan Beijing. It also provides a feasible geophysical approaching to explore the 3-D structure beneath metropolitan cities.