Compression induced formation of a damage zone, which would result in a shear fault in brittle solids is studied. In a compression test of flawed PMMA, an apparent damage zone composed of large number of scattered cracks, which have no intersection but exist closely with each other, is experienced. The damage zone first appears in a vicinity of tips of artificial flaw and then extends gradually with increase of applied compression. The direction of extension of damage zone is observed to incline about 0 30 from the axis of principal compression. A mechanism of the extension of damage zone with increase of applied compression is discussed using a scattered cracking model. It was found that each crack composing the damage zone has a possibility to open due to crack-to-crack interaction and a localized tensile stress appears both inside and outside of the damage zone. The localized tension appeared in the interior of the damage zone may increase crack density, while that of appeared in the exterior of the damage zone could bring an extension of the damage zone.