Abstract: the earth resistivity data show an obvious anomaly at Wudu station before Minxian M_S5.2 earthquake in November 2003. A typical scoop-like variation appeared for the N85°E geoelectric configuration. The regular year variation feature is broken from May 2002, and the value of N73°E configuration rapidly rises from August 2003. The research result indicates that the anisotropic variations of them are remarkable from the time when the anomalies appeared to the time when the earthquake occurred. The maximum change of anisotropic index S′ is more than tow time of the value of regular year variation.

Key words: Minxian M_S5.2 earthquake, Earth resistivity anomaly, Groundwater, Anisotropic index S′