Thiocyanuric acid is the organosulfur compound with the formula (HNC=S)3.

It is a planar molecular as determined by X-ray crystallography.

This arrangement is relevant to the high melting point of the compound.

A modern synthesis begins instead with a preformed ring: cyanuric chloride reacts with sodium hydrosulfide to give table salt and thiocyanuric acid.

This attribute has been exploited by applying thiocyanuric acid and derivatives to treatment of waste waters.