Acids and soluble metal loads resulting from strong acidification preceded by severe drying of acid sulfate soils are fatal soil conditions for agricultural productivity and aquaculture environments. A greater concentration of dissolved Al and Fe after seasonal drought was confirmed in our previous paper using acid sulfate soils in the Mekong Delta. Furthermore, moisture desiccation resulting from land-use change and subsoil excavation for drainage probably promotes soil oxidation followed by acidification. We prepared air-dried soil moisture condition actual acid sulfate soils in the Mekong Delta to evaluate acidification and the release of acids and metals with drying. The pH values of the deepest horizon in the Hydroaquentic Sulfaquepts drastically dropped and greater concentrations of Al and Fe were released with drying. It was a common change from the sulfidic horizon to the sulfuric horizon. A large increase in Al release without a drop in pH after drying was observed in the sulfuric horizons of the Typic Sulfaquept, which developed on the oldest land in the Mekong Delta. Acidification by oxidation of reduced sulfur compounds might be compensated mainly by exchangeable Al and/or by the dissolution of Fe and Al oxides. In contrast, the concentration of Al increased slightly by drying in the sulfuric horizons in the Hydroaquentic Sulfaquept, which developed in the newer delta. The exchangeable basic cations in these soil horizons might still be effective in compensating for the protons produced by the oxidation of pyrite. The difference in the Al released by drying between the two sulfuric horizons might be attributed to the ripeness of the acid sulfate soils. The ripeness of the soil on the older delta might be higher than that on the younger delta. In this study, drying of acid sulfate soils, even in the sulfuric horizon, can promote metal release due to the exchange by protons derived from the oxidation of reduced sulfur compounds. However, further acidification might be compensated by a substantial amount of exchangeable cation and oxide dissolution.