Technical Abstract: Aims: To compare for the first time biofilm formation among strains of Leuconostoc citreum and L. mesenteroides that produce varying types of extracellular glucans. Methods and Results: Twelve strains of Leuconostoc sp. that produce extracellular glucans were compared for their capacity to produce biofilms. 16s rRNA sequence analysis was used to confirm the species identity of these strains, which included four isolates of L. mesenteroides, five isolates of L. citreum, and three glucansucrase mutants of L. citreum strain NRRL B-1355. Biofilm formation was quantitatively measured in commercial flow-cell reactors. All strains identified as L. mesenteroides produce glucans generally similar to commercial dextran. Nevertheless, these strains differed widely in their capacity to form biofilms, with densities ranging from 2.7 to 6.1 log (cfu/cm2). L. citreum strains and their derivatives produce a variety of glucans. These strains exhibited biofilm densities ranging from 2.5 to 5.9 log (cfu/cm2). Conclusions: Although biofilm densities varied widely on a strain-specific basis, no apparent correlations were found with bacterial species or extracellular glucans. Significance and Impact of the Study: Despite the fact that biofilms produced by Leuconostoc sp. are economically important as contaminants of sugar processing plants, very few studies are available on these systems. Results will support further studies to improve control strategies.