A suite of Paleoproterozoic mafic-ultramafic rocks was discovered in the Wuyishan Block in southwest Zhejiang Province through 1:250000 regional geological survey of Quzhou Sheet. These mafic-ultramafic rocks comprising mainly pyroxene hornblendite, hornblendite, plagioclase actinolite, plagioclase pyroxenite and amphibolite are exposed perfectly in Zhangcun Village of Jinhua County and spatially exhibit planar-shaped distribution in Jinhua County and Longyou County. Zircon U-Pb dating with LA-ICP-MS shows that the formation age of pyroxene hornblendite is 1 834±14 Ma (MSWD=0.23, N=16), and that of actinolite is 1 839±17 Ma(MSWD =0.22, N=11), which suggest that these mafic-ultramafic rocks formed during the Paleoproterozoic magmatism. This discovery reveals that the Wuyishan Block was experiencing intraplate extension process at about 1 830 Ma and that the Wuyishan Block might have been a rigid continent at that time so that large-sized brittle fractures could be formed in the interior of the Wuyishan Block and induced basic magmatism resulting from mantle convection. Based on these facts and inference, the authors hold that the Wuyishan Block already had been cratonized at about 1.83 Ga.