Abstract: The Laowan gold deposit is a large-sized deposit recen tly discovered in northem slope of the Tongbai Mountains. It occurs in middle Pr oterozoic metamorphic basic volcanic-sedimentary rocks o f the Guishan Formation. The Laowan granite intrue d in the Laowan fault belt. The orebodies are controlled by granite. The ore grade becomes richer where the granite swells. 　　The genesis of Laowan gold deposit is complex. Some scholars considered that it belongs to the shear zone type. In this paper, in order to make sure t he relationship between the deposit and the granite, a prelimina ry study on　40Ar/39Ar dating has been carried out on three representative samples. These samples are: one q u artz sample from the second ore-forming stage of the deposit, one quartz sample from granite, and one potash-feldspar sample from granite.The　40Ar/39Ar analyses were carried out in Beiji ng Institute of Geology, Academia Sinica, by using the RGA-10 mass spectrometer. 　　The　40Ar/39Ar plateau age and isochrone age for corresponding sam ples are: for the quartz from one deposit, 91.5 and 88.9 Ma, respectively; for t he quartz from granite, 104.0 and 102.8 Ma, respectively; for the feldspar f rom granite, 108.9 and 108.7Ma, respectively. These isochrone ages indicate that the granite and the deposit were formed in late Yanshannian and have very close relationship. 　　The analysis on stress condition for mineralization of the Laowan gold deposit a n d petrogenesis of the Laowan granite suggests that they were formed in a transit ion condition f rom compressive stress to tensile stress or in a mainly tensile stress condition . In this stage, large amount of hydrothermal fluids of different origins appears, which is very favorable for ore deposition.