Chloride ingress is considered as the most responsibility to steel corrosion for offshore concrete structure during service. Fly ash has been shown to effectively enhance the resistance of concrete to chloride penetration. Despite the numerous contributions of investigation regarding the chloride migration behavior of fly ash blended concrete composites by using rapid chloride migration (RCM) test, there is still a lack of critical understanding of curing age effect on the chloride migration in fly ash concrete under RCM testing system. The present study aims to investigate the effect of curing age on the resistance of fly ash blended concrete to chloride ion under RCM test, also considering the factors of water-to-binder ratio and fly ash content at the same time. Based on the RCM tested results, it is found that the effect of curing age condition on the chloride migration resistance is depended on the amount of fly ash incorporated in concrete. Short term curing age can lead to increase the chloride migration coefficient of concrete with low fly ash content. But resistance to the chloride migration can still be enhanced at this curing stage when high percentage of fly ash is supplied. Long term curing age can benefit the chloride migration resistance, regardless of how much fly ash is used in concrete. However, this positive effect becomes less significant when increasing the curing time at the late curing stage. The concrete microstructure is also explored to elucidate the macro-behavior of chloride migration. (C) 2017 Elsevier B.V. All rights reserved.