Abstract: Recently a sequence of strata has been found in the Zhongba stratigraphic area, southern Tibet. It is complete and its contact relationships with the overlying and underlying strata are clear in the Caibalong area, Zhongba County; so it is named the Caibalong Formation. This sequence of strata consists predominantly of metabasalt and amygdaloidal metabasalt, with metabasaltic breccia lavas seen in the lower part and quartz meta-trachyandesite in the upper part. The metabasalt and amygdaloidal metabasalt and the metabasalt and quartz meta-trachyandesite mosdy occur as rhythmic alternating beds, exhibiting the rhythmic characteristics of volcanic eruption. The geochemical characteristics of the metabasalt agree with those of continental rift type volcanic rocks, forming a tectonic environment of the active shelf rift basin, This discovery provides a new important clue to the study of the breakup of the supercontinent Gondwana and opening of the Neo-Tethys.