The newly discovered Neoproterozoic highMg andesites are located at Zhangshudun of the NE Jiangxi ophiolite belt and are dated at a zircon UPb age of 794.8 ± 6.0 Ma. They have variable SiO2 (54.90%~58.45%), CaO (2.46%~6.73%), relatively consistent Al2O3 (15.31%~16.77%, mostly less than 16%) and FeOT/MgO values (0.87~1.20), and show relatively high MgO contents (6.22~8.47%), high Mg# (64~71), which clearly exhibits the diagnostic features of typical highMg andesites. The study samples are enriched in LREE and have slightly negative Eu anomalies. In spider diagram, they show enrichment of LILE (eg. Rb, Ba) while depleted in Nb and Sr elements. These andesites have relatively low Sr abundance and Sr/Y ratios (4.11~7.29), similar to Sanukitoids of the Setouchi volcanic belt in Japan. The zircon Hf isotopes show positive initial epsilon Hf values ranging from +10.3 to +17.8. These geochemical data indicate Zhangshudun highMg andesites should derived from the deplted mantle wedge metasomatized by fluids released from the subducted slab, within an oceanic arc setting. Therefore, it is inferred that the Shuangxiwu arc was away from the southeastern margin of the Yangtze Block, and the Yangtze and Cathaysia blocks had not collided at least at ca.800Ma.