The S receiver function technique was applied to the recordings from 36 broad-band stations in the Tien Shan. The results reveal a pronounced difference in the properties of the lithosphere-asthenosphere of the Tien Shan and those of the neighboring platforms. Beneath the Tien Shan, an upper-mantle lid with an S velocity of about 4.5 km/s is underlain at a depth of about 90 km by a low-velocity zone, where the S velocity drops to 4.1--4.2 km/s. Trends of P and S travel time residuals are consistent with the presence of melt or other liquids in this zone. There is no evidence of any similar layer beneath the platforms. The crust is 55--65 km thick beneath most of the Tien Shan and 45 km below the platforms, although it thins to about 45 km near the Naryn basin in the central Tien Shan.