Abstract: Ultrabasic rocks in northeastern Jiangxi occur on the southeastern side of the deep northeastern Jiangxi fracture zone. They are distributed parallel to the deep fractures. Almost without exception the rock masses occur in the Second Rock Unit of the Upper Subgroup of the middle Proterozoic Shuang- qiaoshan Group. The ultrabasic rocks are closely associated with the basic metalavas and spilite keratophyre series and coexist in the same position and mix with gabbro, diabase and siliceous rocks, argillaceous rocks and carbonate rocks to form a "trinity", whose basic characteristics are similar to the "ophiolite suite". The author considers that the ultrabasic mass in the area belongs to a cold intrusion formed by structural emplacement. The relationships of the ultrabasic. mass and its country rocks are harmonious, indicating that they formed contemporaneously. The ultrabasic rocks were formed prior to the formation of the Dengshan Group, so should be of early Jinningian age.