Efficacy of Carbocisteine in experimental sinusitis in rabbits was evaluated in the morphological and biochemical study. Observations through the light and scanning electron microscopy revealed a marked improvement in sinusitis in the group of rabbits treated with Carbocisteine comparing with those in the control. Degrees of the improvoment tended to increase in a dose response manner. Biochemical research showed that the serum level of L-fucose in the groups treated with Carbocisteine was lower than that of the nontreated group. Based on the results mentioned above, Garbocisteine is considered to be one of the useful drugs for sinusitis.