Thirty isolates of Sclerotium rolfsii, the causal agent of stem rot of groundnut obtained from different Rayalaseema areas of Andhra Pradesh, India were categorized into four groups, on the basis of oxalic acid production in the culture filtrate and severity of patrhogenicity on groundnut seedlings. The group four was more dominant than other groups and highly virulent to groundnut seedlings. There was a positive correlation between oxalic acid production and the virulence of the isolate.