To provide a microetching agent capable of roughening the surface of stainless steel into a uniform rugged shape and to provide a surface roughening method.

This microetching agent for stainless steel is composed of an aq. soln. contg., by weight, 15 to 70% sulfuric acid, a chloride ion source by 0.3 to 9.5% as a chloride ion, a cupric ion source by at least 0.01% as a cupric ion and a thiol compd. by 0.0001 to 1%, and the method for roughening the surface of stainless steel uses the above aq. soln.