A microbial colony that contained a marked amount of cellulose was isolated from vineyard soil. The colony was formed by the associated growth of two bacterial strains: a cellulose-producing acetic acid bacterium (st-60-12) and a lactic acid bacterium (st-20). The 16S rDNA-based taxonomy indicated that st-60-12 belonged to Gluconacetobacter xylinus and st-20 was closely related to Lactobacillus mali. Cocultivation of the two organisms in corn steep liquor/sucrose liquid medium resulted in a threefold higher cellulose yield when compared to the st-60-12 monoculture. A similar enhancement was observed in a coculture with various L. mali strains but not with other Lactobacillus spp. The enhancement of cellulose production was most remarkable when sucrose was supplied as the substrate. L. mali mutants for exocellular polysaccharide (EPS) production were defective in promoting cellulose production, but the addition of EPS to the monoculture of st-60-12 did not affect cellulose productivity. Scanning electron microscopic observation of the coculture revealed frequent association between the st-60-12 and L. mali cells. These results indicate that cell-cell interaction assisted by the EPS-producing L. mali promotes cellulose production in st-60-12.