Thinning of the crust of more than 10 km is a major feature of typical continental rifts such as the East African (EAR) and Rio Grande (RGR) rifts. However, numerous previous studies across the Baikal rift zone (BRZ), which has similar surface expressions and tectonic history, and more active seismicity relative to EAR and RGR, have resulted in contradicting amount of thinning, ranging from almost none to more than 10 km. We measure crustal thickness by stacking teleseismic receiver functions beneath 51 sites on the southern and central parts of the BRZ and adjacent Siberian Platform and Sayan-Baikal-Mongolian Foldbelt. Our measurements reveal that beneath the southern part of the Platform, the average crustal thickness is about 38 km, which is about 7 km thinner than that beneath the Foldbelt and the un-rifted part of the BRZ. The thinnest crust, 35 km, is found beneath the central part of the rift, and represents a significant thinning of about 10 km relative to the un-rifted parts of the BRZ.