To investigate the effects of ammonia concentration in ACFA (Ammonia Contaminated Fly Ash) on the mortar and concrete, measurements of several properties for mortar and concrete mixtures where 10∼15 % of the cement replaced with ACFA containing ammonia of from 0 to 620 ppm were studied. Test results showed that compressive strength of mortar and concrete decreased, and setting time of mortar delayed with increasing the replaced amount of ACFA for cement as well as ammonia concentration in ACFA, due to impacts of aggressive ammonium and sulfate ions. Based on XRD, SEM, and TG-DSC analysis of the mortars hydrates phase, it can be concluded that the main components of the mortar hydrate are C-S-H and CaCO3. In the case of the presence of ammonia in mortar, C-S-H and ettringite formation was suppressed, and hydration reaction rate was delayed because free water in mortar was decreased. Relative dynamic elastic modulus of concrete containing 15% ACFA replaced for cement was lower than that of no-fly ash concrete. As the ammonia concentration in ACFA, and a replaced amount for cement were increased, the relative dynamic elastic modulus of concrete was decreased indeed.