2-Hydroxy-1, 2-dihydro-3H-indol-3-ones 3 were obtained from 1, 2-dihydro-3H-indol-3-ones 2 by using various conditions (m-CPBA or sodium azide) depending on substituent in 1- position. The reactivity of hydroxyketones 3 is examined and oxidation of 1-(phenylsulfonyl) indole by m-CPBA is described.