Abstract: The lower boundary of the Shuangqiaoshan Group in Jiangxi is a long stanging problem. Through recent 1∶50 000 regional surveys and study on the Lushan area, a suite of very thick bedded metaconglomerate of complex composition has been found in the vicinity of Huangling, Xingzi county. On the basis of the gravel composition, fabrics and regional distribution of the metaconglomerate coupled with the marked difference in metamorphism and deformation of the upper part （Shuangqiaoshan Group） and lower part （Xingzi Group Complex） of the suite, the author holds that the metaconglomerate should be assigned to the base of the Shuangqiaoshan Group. It is evidence of the unconformity between the Middle Proterozoic Shuangqiaoshan Group and the underlying Lower Proterozoic Xingzi Group Complex. Owing to the influence of tectonic superimposition and reworking at the late stage, both show fault or hidden unconformable contact relationships at present.