Abstract: Much attention has long been paid to the chronology of rapakivi granite in Miyun because it formed simultaneously with the destruction of the North China craton and initiation of the Mesoproterozoic Yanliao rift. High-quality SHRIMP ages were lacking though some data available could be used as reference. The authors for the first time obtained a weighted mean SHRIMP U-Pb zircon age for the rapakivi granite by telemetry at the Ion Microprobe Center, Curtin University, Western Australia, and got a high-quality weighted-mean SHRIMP age of 1685±15 Ma. This age suggests that the Yanliao rift was initiated at 1700 Ma. This age provides an important base for calibrating the age of the lower boundary of the Changchengian System.