The formation age of basalts from the lowermost Neoproterozoic Chengjiang Formation in the western Yangtze Block has not been determined yet. In this paper, field investigations and detailed petrologic and geochronologic researches were carried out on basalts of the lowermost Chengjiang Formation from the Luoci area, Wuding, and the results show that the formation age of basalts from the lowermost Chengjiang Formation is 804±6 Ma, which further confirms that the lower age limit of the Chengjiang Formation should be about 800 Ma. Petrologic studies show that basalts from the lowermost Chengjiang Formation have lower SiO₂ content and high K₂O+Na₂O and TiO₂ content, which indicates that their formation should be attributed to alkaline basalts developed in the continental rift. Combined with regional relevant research data, it is suggested that there possibly existed an episodic bimodal magmatic rock belt that lasted from ～800 Ma to 725 Ma along the western Yangtze Block. It is thus held that basalts of the Chengjiang Formation as well as volcanic rocks of the Suxiong Formation were formed by ~800 Ma bimodal magmatic activity, and that this bimodal magmatic rock belt might have been developed in the continental rift. Moreover, the ages of captured zircons from the basalts indicate that there were multi-stage regional tectonic-thermal events along the western Yangtze Block, which took place at 2.5 Ga, 1.8～1.6 Ga and 1.0 Ga.