Allantoic acid is an organic compound with the chemical formula C<sub>4</sub>H<sub>8</sub>N<sub>4</sub>O<sub>4</sub>. It is a crystalline acid obtained by hydrolysis of allantoin.
In nature, allantoic acid is produced from allantoin by the enzyme allantoinase (encoded by the gene AllB (Uniprot: P77671) in Escherichia coli and other bacteria).