Abrasive water jet processing is being developed in relation to the developments in engineering materials science. In this study, brass-353 (alpha + beta brass), 99% pure aluminum, Al-6061 aluminum alloy, AISI 304, AISI 1030 and cold working tool steel (D3) materials were drilled with AWJ. The effects of thickness and material type on the drilling time were investigated and discussed. Hardness of the base materials and the drilled surfaces were measured and assessed. Results of the hardness test showed that there is not much difference between the drilled surface and the base material hardness. Micro photographs taken from the drilling surfaces show that drilling does not affect the micro structure and mechanical properties of the material. (C) 2008 Elsevier Ltd. All rights reserved.