Abstract: This paper studies antifungal activity of Cinnamaldehyde against some common fungi and compares with that of Ketoconasolc.The results showed the MIC of Cinnamaldehyde against yeast and yeast-like fungi ranged from 1.95 to 62.50μg/ml,C.krusei and C.tropicalis were the most sensitive fungi to this dnig.The MIC against dermatomyces and deep fungi ranged from 7.82 to 125.00μg/ml,and T.viloacettm was the most sensitive strain.Time-inhibition of this drug against 10 isolates of C.albicans from different patients was also studied.The lowest antifungal point occurred 8 hours after incubation.SEM and TEM examination demonstrated morphologic change and cell wall impairment of C.albicans,T.mentagrophytes and S.schenckii after they were treated with Cinnamaldehyde.