A primary study was made experimentally and numerically of spherical underwater shock wave focusing and high pressure generation in an ellipsoidal cavity. Spherical shock waves were produced by microexplosion of silver azide or PETN of 10 to 100 mg. The ellipsoidal cavity has major and minor axes of 700 and 500 mm, respectively. The focused pressure was measured along the major axis by PVDF pressure gauges. By exploding a 100 mg PETN pellet the peak pressure at 8 kbar was obtained near the second focal point. The TVD finite difference numerical simulation was also conducted. Good agreement was obtained between the experiment and simulation.