Thiosemicarbazide is the chemical compound with the formula H2NC(S)NHNH2.

A white, odorless solid, it is related to thiourea (H2NC(S)NH2) by the insertion of an NH center.

These feature an organic substituent in place of one or more H's of the parent molecule.

According to X-ray crystallography, the CSN3 core of the molecule is planar as are the three H's nearest the thiocarbonyl group.

[4] Formylation of thiosemicarbazide provides access to triazole.