The Al tridecamer (Al-13) is the most active species in Al-based coagulant. Solid Al-13 samples with high purity can be separated and purified using an ethanol-acetone fractional precipitation method. In this paper, we present the characterization of the stability of solid Al-13 under different storage conditions as well as the performance and behavior during the coagulation process. The results show that solid Al-13 has good solubility and stability, and the original distribution of the Al species and the Al-13 content can be maintained stably during the dissolution, dilution and storage processes. During the studied storage period, either as liquids or solids, the Al-13 neither degrades nor polymerizes. The Al-13 is prone to aggregation at high concentrations, but the aggregates dissociate rapidly upon dilution. Compared with other Al species, the Al-13 has better charge-neutralizing ability and can destabilize particles suspended in water more rapidly. The Al-13 can decrease the optimum dosage, improving the coagulation performance at lower dosages. The coagulation mechanism of Al-13 depends on its dosage and the coagulation pH, and is dominated by the charge-neutralization and enmeshing-sweeping mechanisms. (C) 2011 Elsevier B.V. All rights reserved.