Located in the southwestern part of the Dayaoshan uplift，the Longtoushan porphyry gold deposit, Gui county, Guangxi, is closely related to the Late Yanshanian rhyolitic porphyry and graniteporphyry within the orefield. The authors carried out with high decision SHRIMP dating technique UPb chronology of zircons from the rhyolitic porphyry and graniteporphyry and gained ideal ages of 103.3±2.4Ma（95% confidence，MSWD=2.1）and 100.3±1.4Ma（95% confidence，MSWD=0.40），respectively. The result shows that diagenetic mineralization of the Longtoushan gold orefield happened during the Middle to Late Cretaceous. Based on the zircon ages，the authors concluded that the rhyolitic porphyry and graniteporphyry resulted from the same magmatic event, but only one mineralization event occurred in the orefield rather than two stages of diagenetic mineralizations as the earlier researches believed.