Griseofulvin derivatives, dl-6'-demethyl-6'-ethylgriseofulvin (dl-5) and dl-6'-demethyl-6'-phenylgriseofulvin (dl-6) were prepared by application of a synthetic method developed by us. Antifungal activity of these derivatives decreased in the order of dl-griseofulvin (dl-1)>dl-5»dl-6 (inactive). The reaction of these derivatives with ethanethiol gave two types of compounds, 2'-(ethylthio)griseofulvin (15) and 4'-(ethylthio)isogriseofulvin (16). The relationship between the ratios of isolated yield of 15 and 16 and antifungal the activity of griseofulvin derivatives is discussed.