To investigate the effects of free radical, 1, 1-Diphenyl-2-picylhydrazyl(DPPH), on cochlear blood flow.Twenty guinea pigs were divided into 3 groups at random, 6 for control group, 6 for 1 mmol/L of DPPH group and 8 for 0.1 mmol/L of DPPH group. 2 microliters vehicle or drugs were dropped into round window membrane. Cochlear microcirculation was monitored by laser Doppler flowmeter and the mean arterial blood flow(MABP), which transferred by pressure conductor sensor and preamplifier, was simutaneously recorded by a computer.MABP was stable throught the experiment. Cochlear blood flow increased 12.49% (P < 0.05) in 1 mmol/L group, and decreased 3.02% (P < 0.05). In control group cochlear microcirculation had no significant changes.DPPH has effects on cochlear microcirculation. The mechanism still need to be explored later.