The quartz-aluminosilicate veins in the Hamadan region consist of quartz with one, two or three polymorphs of aluminum silicate )andalusite, kyanite and sillimanite(. In some veins other accessory minerals (i.e. garnet, chlorite, muscovite, staurolite, biotite and plagioclase) are present. The petrogenesis of these veins and their country rocks have been previously described; this paper studies oxygen isotope ratios of co-existing quartz and Al₂SiO₅ to determine formation conditions and genesis of these veins. The δ ¹⁸O/ ¹⁶O values of quartz, andalusite, kyanite and sillimanite range from: +(16.8-17.1)‰, +(14.2-14.5)‰, +14.1‰ and +14.6‰, respectively. These results indicate a possible metamorphic origin for fluids responsible for the formation of these veins and magmatic origin of fluids is unlikely. The estimate temperature for the formation of veins is about ~ 480-550 ^oC, a range thet consistent with petrographic observations in the veins and previous thermometry results on host rocks of veins.