Influence of pulse width and water conductivity on decolorization of organic dye by discharge inside bubble in water was investigated. Two types of pulsed power generator, a magnetic pulse compression circuit and an inductive-energy storage system using semiconductor opening switch, were used to generate high voltage pulses with various pulse widths. Indigo carmine was employed as a specimen to evaluate decolorization efficiency. Argon gas was used to identify the influence of hydroxyl radicals produced by the discharge on decolorization efficiency. Energy efficiency for the decolorization increased with decreasing the pulse width owing to the reduction of ohmic loss.