A metal halide lamp comprises a discharge tube of transparent ceramic in which a discharge metal is sealed, the discharge tube having a main cylindrical portion, ring portions provided at both ends of the main cylindrical portion, and tubular cylindrical portions provided at the ring portions; and a pair of electrodes inside the discharge tube; wherein a wall thickness .alpha. (in mm) of the main cylindrical portion satisfies the relation0.0023.times.W+0.22.ltoreq..alpha..ltoreq.0.0023.times.W+0.62,and a wall thickness .beta. (in mm) of the ring portion satisfies the relation0.0094.times.W+0.5.ltoreq..beta..ltoreq.0.0094.times.W+1.5,wherein W is the lamp power expressed in Watt. Alternatively, the discharge tube is air-tightly enclosed in the outer tube; the outer tube is filled with a gas comprising nitrogen gas; and the wall thickness .alpha. (in mm) of the main cylindrical portion satisfies the relation0.0023.times.W+0.12.ltoreq..alpha..ltoreq.0.0023.times.W+0.62,and the wall thickness .beta. (in mm) of the ring portion satisfies the relation0.0094.times.W+0.3.ltoreq..beta..ltoreq.0.0094.times.W+1.5,wherein W is the lamp power expressed in Watt. Thus, a metal halide lamp can be obtained that has a stable lifetime and considerably increased lamp efficiency compared to conventional high-color-rendition high-performance metal halide lamps using a quartz discharge tube.