Alkaline biosolids may be suitable as a liming amendment for acid soils. The efficacy of two alkaline biosolids, lime-stabilized sewage sludge (LS) and N-Viro Soil (NV), for remediating soil acidity and Al toxicity in strongly acid soils were evaluated. For comparison, soils were also treated with unlimed anaerobically digested sewage sludge (SS) and agricultural lime (L). Three acid soils were amended with LS, NV, SS, and L and incubated at 25°C. Soil solution was extracted at 1, 30, 90, and 180 d incubation and analyzed for pH, electrical conductivity (EC), dissolved organic carbon (DOC), Al, Mn, Ca, Mg, Na, K, F, Cl, PO4, NO3, and SO4. In general, soil pH increased linearly with amendment rate for all soils and all amendments. The magnitude of increase in soil pH after 6 mo for the four amendments followed the order L ≃ NV>LS>>SS. All amendments decreased soluble Al, but lime-containing amendments (LS, NV, and L) decreased soluble Al below detection limits (<0.4 mmol L−1). The largest decreases in exchangeable Al were associated with lime-containing amendments. Lime-containing amendments reduced soluble Mn but unlimed sewage sludge had no effect on soil solution Mn. Soluble Al speciation using MINTEQA2 showed that all rates of lime-containing amendments (LS, NV, and L) decreased Al3+ activity to nontoxic levels (<10 mmol L−1). Saturation indices indicated sewage sludge amendments may have resulted in precipitation of Al as alunite [KAl3(OH)6(SO4)2·H2O]. Although SS decreased phytoavailable Al, alkaline biosolids caused greater reductions in potentially phytotoxic Al than nonalkaline biosolids (SS).