Cell-free extracts of mycelia and sclerotia of Sclerotinia sclerotiorum (Lib.) D By. grown on synthetic liquid medium with various carbon sources contained trehalase (α,α′-glucoside 1-glucohydrolase; EC3.2.1.28) activity. The enzyme was not usually detected in the culture filtrate. Treatment with ammonium sulfate or MnSO4 and alumina resulted in a 2- to 3-fold purification. The optimum pH (5.0), K m with trehalose (1.7×10-3 M) and other properties are within the range reported for trehalase from other fungi.