A new aluminosilicate glass (AL) has been developed, which possesses excellent melt-ability and low thermal expansivity. The light transmittance and the thermal expansion coefficient of AL well met the requirements for low thermal expansion photomask substrates (LTE) designated by SEMI. The other major properties of AL for photomask use such as chemical durability, mouse-nips, scratch resistance, and electrical resistivity were mainly studied in comparison with a conventional LTE and a synthetic quartz glass (QZ). Both of the weight losses of AL due to acid and alkaline solution attacks were approximately a half those of the conventional LTE, indicating that pattern damages produced during mask cleaning processes with such chemicals are improved. It was comfirmed that mousenips resulted from a reaction between chromium film and sodium ions in AL were not produced under a heat-treatment condition of 200°C, 60 min. From a comparison of the deformation/fracture parameters between AL and QZ, the mechanical damages for AL were shown to be considerably slighter than QZ in spite of the higher microhardness of QZ. The lower electrical resistivity of AL revealed less dust contamination potential than QZ. The defect level and the improved properties of AL were discussed in terms of optical microlithography and photomask application.