We conducted a time course experiment on mycelial cultures of Laetiporus sulphureus var. miniatus. The strain showed significant survival in an initial pH range of 2.0 to 7.0 for 24 days, during which time oxalic acid was accumulated. A structural analysis of purified exopolysaccharide suggested that it contained 96.1% glucose, and the mode of linkage was mainly4${ ightarrow}$Glcp-(1${ ightarrow}$units, with branches at the C-6 position consisting of a Glcp-(1${ ightarrow}$4) linked side chain. An exopolysaccharide purified from the acidophilic strain was added to cultured U937 cells, resulting in significantly increased transcription levels of p53 and p21 genes.