Source parameters of the 4 June 2000 southern Sumatra, Indonesia, earthquake (Ms 8.0) were estimated from teleseismic body waves recorded by long-period seismograph stations of the global seismic network. The analysis shows that the earthquake had a mechanism with a strike of 199°, a dip of 82°, and a rake of 5° and ruptured unilaterally from the northeast to the southwest, nearly perpendicular to the Java Trench. The focal mechanism of mainly left-lateral strike slip, with a small thrust component, explains well the reason why no tidal waves were generated by this great earthquake. The double-couple component of this earthquake was 1.5 × 1021 Nm, the compensated linear-vector-dipole component was 1.2 × 1020 Nm, and the explosion component was 5.9 × 1019 Nm. The analysis indicates that the source duration was about 16 sec. The fault area is about 95 km in length and 60 km in width. The average static slip is estimated to be about 11 m, and the average static stress drop, 90 MPa.