Three-dimensional P-wave velocity structure of the crust and upper most mantle beneath the Koyna Seismic Zone (KSZ) was determined by inverting 780 P-wave teleseismic travel times recorded by a 20 station digital network. The velocity image obtained through damped least square was tested for its resolution using checkerboard approach. The results of the inversion show strong lateral velocity variations of 6% to 7% within the study region. A high velocity anomaly (2% to 5%) in the upper and lower crust beneath the KSZ is flanked by lower velocity (-2% to -5%) anomalies on either side. The correlation of high-velocity with the seismic zone suggests that the earthquakes are occurring in more rigid rocks with increasing ability to store strain energy and release it as brittle failure. ¿ 2000 American Geophysical Union