Though many worldwide attempts to establish radon anomalies in soil and groundwater as precursors for major earthquakes are made, yet practically no such work has been reported for micro-earthquakes in a Stable Continental Region (SCR). From the continuous radon measurements for five months at a depth of 1 m in fractured granitic area, we report for the first time that enhanced radon concentration preceded seventeen hours the occurrence of micro earthquake. The peak radon level (twice the normal concentration) was reached thirteen hours before the occurrence of the event and decayed exponentially during the next 5 days to come to normal level. This radon precursor pertains to a dry period, unaffected by meteorological factors, thus exemplifies clearly its association with micro earthquake.