Broadband data from the recently installed Ulaanbaatar Seismic Network provides a good opportunity to study the structure of the crust and upper mantle beneath Ulaanbaatar region, Mongolia. A receiver function analysis was used to estimate shear wave velocity models beneath 15 broadband stations in the study area. Seismic waveform data from 230 teleseismic events were processed to obtain receiver functions. Stacked receiver functions were inverted for 1D shear wave velocity models with genetic algorithms. The resulting models indicated that the average crustal thicknesses were 44 – 45 km for stations in mountainous areas and 40 – 42 km in other areas. This difference in crustal thickness between mountainous and other areas can be explained by isostatic compensation. Some resulting models had low velocity layers at depths of 5 - 12 km. Investigation of the nature of the low velocity layers would be the next stage of research in this area.