Abstract: The NS or NE-SW trending Gaoligong metamorphic belt lying in southwest Yunnan Province is distributed along west Gaoligongshan strike-slip shear zone. It is composed of high-degree metamorphic rock, which has been considered as Precambrian metamorphic basement before. In this paper, U-Pb zircon dating was carried out by using LA-ICP-MS for granitic mylonite from the Gaoligongshan shear zone. It yielded the weighted average age of 41.9Ma±1.0Ma from magma zircons and that of 38.4Ma±2.1Ma from the metamorphic overgrowth rims of zircon, respectively. Combined with regional geological background, geological evolution, rock fabric and geochronological data, this paper has drawn the conclusion that the granitic mylonite was crystallized at 42Ma and underwent mylonitization at 38Ma, indicating that the Gaoligong strike-slip shear zone was active as a dextral strike-slip shear zone at least from 38Ma.