In this work, the durability of glass fiber reinforced mortar (GFRM) wasexperimentally investigated. The evaluation was based on the performance of material under three mechanical tests (compression, indirect tension and flexure). The GFRM specimens were exposed to the effect of four-environmental attack. These include,sulfate, chloride, air, and water. The specimens were submerged in two solutions of magnesium sulfate of 7% concentration and sodium chloride of 7% concentration.The specimens were tested after 28, 180, 360 and 540 days. The effect of fiber volume fraction, (Vr =0, 1, 2, 3 %) was considered. The effect of using sulfateresistant cement and addition of 10% silica fume to ordinary Portland cement on the durability of the GFRM was undertaken. The durability was measured by comparing the strength of specimens submerged in the aggressive solutions to that stored in fresh water.The result of this work indicated that the compressive strength of GFRM specimens increases with increasing fib er volume fraction, Vr % up to 1 % for specimens stored in air, water and chloride. For specimens stored in sulfate, the compressive strength isalmostely unchanged with fiber volume fraction. For un-reinforced mortar specimens,the specimens stored ill chloride give the highest cornpressive strength, while fiber reinforced specimens stored in water give the highest compressive strength. Thespecimens stored in sulfate give the lower relative compressive strength comparedwith other media. The matrix strength is responsible fori the composite compressivestrength. Addition of 1 % fiber volume fraction increase the tensile strength by about171% after 28 days for the specimens stored in air. There is a general increase in thetensile strength with increasing fib er volume fraction, V r% for all storage media andstorage age. The rate of enhancement in the tensile strength with increasing fibervolume fraction for specimens stored in air is higher than that for specimens stored inwater. The composite tensile strength is fib er control property. Flexural strengthincrease with increasing fiber volume fraction, V 1’/0 and storage age for all storagemedia. This increase reach to 137% after 28 days with Vr =1%. The highest flexuralstrength is recorded for specimens stored in water for all storage ages and differentfib er volume fraction. The specimens stored in sulfate give the lowest flexuralstrength up to storage age of 180 days irrespective of control specimens where, thespecimens stored in chloride give the lowest flexural strength. Specimens stored insulfate has a brittle behavior in the load - deflection behavior and has the lowesttoughness comparing with specimens stored in other media while the highesttoughness as measured by the area under p-S curve was for the specimens stored inwater. The presence of fiber increases the work required to fracture the GFRMspecimens and altered their failure mode from a brittle to more ductile failure. Theaddition of 10% silica fume of cement weight enhances the mechanical properties ofthe specimens stored in water media at all ages. For specimens stored in sulfate themechanical properties enhances with the addition of 10% SF up to 180 days and afterthat they decreases. Sulfate resistant cement shows high strength in sulfate mediacompared to those specimens stored in water media especially in compressive andtensile strengths without fib er volume fraction but it has a negative effect on theflexural strength. Specimens made with OPC + 10% SF had the highest compressivestrength compared to those made with sulfate resistant cement or OPC, for specimensstored in water media with or without fiber. In sulfate media, SRC gives the highestcompressive strength. GFRM Specimens made by OPC + 10% SF had the highestvalues of the tensile strength at early ages up to 180 days.