The effect of fineness of fly ash on mechanical properties and alkali-silica reaction resistance of cement mortar mixtures incorporating fly ash has been investigated within the scope of this study Blaine fineness of fly ash has been increased to 907 m(2)/kg from its original 290 m2/kg value by a ball mill. Test samples were prepared by replacing cement 20, 40 and 60%, with finer and coarser fly ashes and kept under standard and steam curing conditions until testing. Test results showed that grinding process improved the mechanical properties of all samples significantly. The beneficial effect of grinding fly ash. may increase utilization of this by-product in precast and ready-mix concrete industries Incorporation of fly ash with different fineness values and ratios also decreased the expansions to harmless levels of cement mortars due to alkali-silica reaction. (C) 2009 Elsevier B V. All rights reserved