RF method is now a well-known tool for studying crustal and upper mantle structure when such a complete data set is available. We compute P receiver functions to investigate the upper mantle discontinuity beneath the Northwest of Iran. We selected data from teleseismic events (Mb ? 5.5, 30 ?>? > 95?) recorded from 1995 to 2008 at 8 three component short period stations from Tabriz Telemetry Seismic Network with high signal-to-noise ratio. The P to S converted phases from 410 and 660 km discontinuities are delayed by more 2 and 1 s with respect to IASP91 global reference model, indicating that the upper mantle above 410 km is 3-4% slower and high temperature than the standard earth model. Because the 410 and 660 km discontinuities do not show the same delay, the transition zone is also could be thinner. This could mean that the upper mantle in the region is still influenced by several geodynamical processes involving rifting, uplift and magmatism.