This study was conducted to investigate the relationship between pH and the toxicity of sulfur dioxide against homo- and hetero-lactic acid bacteria isolated from American acidic wines. Malolactic fermentation was found to be growth-associated in homo- and hetero-lactic strains. The pH of CBB broth had an insignificant effect on the specific death rate of these strains; the concentration of molecular sulfur dioxide had a great effect on the specific death rate and malate degradation. Laboratory or freshly isolated strains were exposed to various concentrations of free sulfur dioxide at pH 3.8 and 3.4. At pH 3.4, sulfur dioxide was more effective against lactic acid bacteria than at pH 3.8 since more was present as molecular sulfur dioxide and causing an increase in the specific death rate. Pediococcus strain BB was more resistant to sulfur dioxide than those hetero-lactic fermentation strains such as Leuconostoc oenos PSU-1 and ML-34. The effect of sulfur dioxide concentration on the viability of L. oenes ML-34, PSU-1, and Pediococcus strain BB appeared to be biphasic. No or little L-malic acid was degraded when the homo- and hetero-fermentative strains were killed by sulfur dioxide.