Isothiazole, or 1,2-thiazole, is an organic compound consisting with the formula (CH)₃S(N). The ring is unsaturated and features an S-N bond. The isomeric thiazole, where the S and N are not directly bonded are far more common.

Isothiazones are produced by oxidation of enamine-thiones. The ring structure of isothiazole is incorporated into larger compounds with biological activity such as the pharmaceutical drugs ziprasidone and perospirone.