Due to discrepancies regarding the effectiveness of lufenuron in treating dermatophytosis caused by Microsporum canis the effect of this drug was checked in 46 cats (30 with cutaneous lesions and 16 asymptomatic carriers) treated in the Veterinary Hospital of the Federal Rural University of Rio de Janeiro, Brazil. The diagnosis was based on Wood's lamp examination and fungal cultures. Biopsies were only performed in symptomatic animals. The animals were treated with lufenuron (120mg/kg every 21 days), for 4 times. The drug was efficient in 29 of the 30 affected felines and as well as in all of the asymptomatic carriers. The cat that did not respond, had received several dexametazone doses prior to the treatment with lufenuron. The drug was given to one animal during the first stages of pregnancy and no abnormalities or neonatal disorders were found in any of the kittens. None of the treated animals showed side effects. Twenty days after the last administration of lufenuron, 45 of the studied animals (98%) had negative fungal culture. The cost of treating dermatophytosis with lufenuron is a little higher than with ketoconazole, but the drug has some advantages regarding its practicability and security. The correct drug prescription and animal's medication as well as environmental decontamination are very important for the success of the treatment.