Data now available on the Koyna earthquake have been studied in detail. Different origin times and epicenters given by India Meteorological Department and Central Water and Power Research Station, field evidences and nature of the seismograms for this earthquake suggest a multiple event. A fault plane solution has been obtained by using the sense of first motions. Seismicity in Koyna region has been found to increase with the increase of water level in the reservoir and vice-versa with a certain time lag. The two major earthquakes of this region have similar foreshock-aftershock pattern, corresponding to type 2 of Mogi's (1963) models. Aftershocks of this earthquake are related by a function Log N = a + bM, value of b being −0.8. Possibility of predicting maximum expected magnitude at a certain seismic activity level of Koyna region has been also pointed out.