The controls of soluble Al concentration were examined in three situations of acid sulfate conditions: 1)experimental acid sulfate conditions by addition of varying amounts of Al(OH)3 (gibbsite) into a sequenceof H2SO4 solutions; 2) experimental acid sulfate conditions by addition of the same sequence of H2SO4solutions into two non-acid sulfate soil samples with known amounts of acid oxalate extractable Al; and3) actual acid sulfate soil conditions. The experiment using gibbsite as an Al-bearing mineral showed thatincrease in the concentration of H2SO4 solution increased the soluble Al concentration, accompanied bya decrease in the solution pH. Increasing amount of gibbsite added to the H2SO4 solutions also increasedsoluble Al concentration, but resulted in an increase in solution pH. Within the H2SO4 concentration rangeof 0.0005～0.5 mol L-1 and the Al(OH)3 range of 0.01～0.5g (in 25 mL of H2SO4 solutions), the input ofH2SO4 had the major control on soluble Al concentration and pH. The availability of Al(OH)3, however, wasresponsible for the spread of the various sample points, with a tendency that the samples containing moregibbsite had a higher soluble Al concentration than those containing less gibbsite at equivalent pH levels.The experimental results from treatment of soil samples with H2SO4 solutions and the analytical results ofacid sulfate soils also showed the similar trend. The controls of soluble Al concentration were examined in three situations of acid sulfate conditions: 1) experimental acid sulfate conditions by addition of varying amounts of Al (OH) 3 (gibbsite) into a sequence of H2SO4 solutions; 2) experimental acid sulfate conditions by addition of the same sequence of H2SO4solutions into two non-acid sulfate soil samples with known amounts of acid oxalate extractable Al; and3) actual acid sulfate soil conditions. The experiment using gibbsite as an Al-bearing mineral showed that increase in the concentration of H2SO4 solution increased the soluble Al concentration, accompanied bya decrease in the solution pH. Increasing amount of gibbsite added to the H2SO4 solutions also increased soluble Al concentration, but resulted in an increase in solution pH. Within the H2SO4 concentration range of 0.0005-0.5 mol L-1 and the Al (OH) 3 range of 0.01-0.5 g (in 25 mL of H2SO4 solutions), the input of H2SO4 had the major control on soluble Al concentration and pH. The availability of Al (OH) 3, however, was, for the spread of the various sample points, with a tendency that the samples containing more gibbsite had a higher soluble Al concentration than those containing less gibbsite at equivalent pH levels. The experimental results from treatment of soil samples with H2SO4 solutions and the analytical results of acid sulfate soils also showed the similar trend.