PURPOSE: To prepare the titled compound in high yield and purity, at a low cost, by reacting 1-carboxymethyl-5-mercapto-1,2,3,4-tetrazole with hydrogen peroxide solution using water as a solvent, and neutralizing and removing the by-produced sulfuric acid.

CONSTITUTION: 1-Carboxymethyl-1,2,3,4-tetrazole can be prepared by (1) adding 3.0W4.0mol of a 10W35% aqueous solution of hydrogen peroxide dropwise to an aqueous solution of 1mol of 1-carboxymethyl-5-mercapto-1,2,3,4-tetrazole, or to the reaction liquid or waste water containing 1mol of the above compound and discharged from the process for preparation of 1-carboxymethyl-5-mercapto- 1,2,3,4- tetrazole, and (2) neutralizing the by-produced sulfuric acid with an alkali metal hydroxide such as NaOH, KOH, etc. or an alkaline earth metal hydroxide such as Ca(OH)2, etc. and removing the neutralized product from the system.

EFFECT: Simple and safe operation.