This paper discusses the neutralization of concrete of port structures under the severe weather and marine environments. Fourteen structures which were located at 8 ports and were from 4 years to 14 years old were examined. Specimens were taken by means of core boring at the top surface of structures and average depths of neutralization were measured by using phenolphthalein solution as reagent. From test results, the average depth of neutralization for a long term was presumed. Then, following several factors which seemed to affect the neutralization of concrete were examined ; the soaking condition of concrete in the sea water, usage of admixture (fly ash), weight of cement per unit volume of concrete and water cement ratio.