Sulfoacetaldehyde sulfo-lyase, which decomposes sulfoacetaldehyde to sulfite and acetate, was extracted from a bacterium grown on taurine, and purified, and characterized. A method for assay of enzyme activity was devised on formation of a bisulfite adduct with benzaldehyde. The enzyme was purified 14-fold from an extract of cells grown on taurine and appeared homogeneous on disc-electrophoresis. The molecular weight of the enzyme was estimated to be 85,000 by gel filtration. The enzyme required thiamine pyrophosphate (TPP) and Mg2+ for activity and preincubation with TPP and Mg2+ was required for maximum activity. The optimum pH for activity was 7.5. The Km value for TPP was determined to be 2.7 muM and that for sulfoacetaldehyde to be 5.0mM. Sulfite was produced only from sulfoacetaldehyde among a variety of sulfonates tested. rho-Chloromercuribenzoate, EDTA, and sulfite, a reaction product, inhibited the enzyme reaction. The enzyme seemed to be inducible, since activity was found in extracts of cells grown on taurine but not on peptone.