Abstract: The Guandiping biotite diorite outcrops in the Mianlue suture zone, located in the western part of the Guangt oushan granite pluton. The biotite diorite is mainly consisted by plagioclase, bhrnblende and biotite, with slightalt eration. LA-ICP-MS dating of zircon U-Pb yeilds a weighted meanage of 220.5Ma ±3.1Ma (MSWD)=0.66, 2σ), which is considered representing the crystal lizing age of the Guandiping diorite pluton. This age is similar with the emplacement age of the biotite-plagioclase granite (216Ma±2Ma) from the Guang to ushan Pluton in the surroundings, it can be inferred that the Guandiping biotite diorite pluton was formed in post-collisio nalsetting.