Alkali Silica Reaction (ASR) is a chemical reaction which affects both strength and durability of concrete. ASR occurs due to a chemical reaction between alkali oxides presents in the cement paste and reactive silica in aggregate. This reaction could lead to the volume expansion, cracking, loss of strength and potential failure of the concrete. This research aimed to investigate the potential alkali silica reactivity on geopolymer concrete. Specimens were prepared using Class F fly ash as binder while sodium hydroxide and sodium silicate as alkaline activators. ASTM C1260 was adopted to determine potential alkali silica reactivity by measuring the length change of mortar bar as well as the decrease in compressive strength test. Results show that fly ash based geopolymer concrete is less vulnerable to ASR as the expansion of mortar bar is below the threshold of ASTM standard limit which is 0.10 of expansion. In term of strength, the geopolymer concrete did not reduced instead it increased. From the results, it has indicated that both tests ensure that the durability of geopolymer concrete is excellent and can withstand a long life span. © (2014) Trans Tech Publications, Switzerland.