This document specifies the requirements, test methods, inspection rules, marking and accompanying documents, packaging, transportation and storage of D-p-methylsulfonylphenylserine ethyl ester (D-ethyl ester) by-product anhydrous sodium sulfate. This document applies to the sodium sulfate aqueous solution produced in the production process of D-p-methylsulfonylphenylserine ethyl ester, and the anhydrous sodium sulfate obtained after decolorization, concentration, etc., which is mainly used for cement additives, printing and dyeing, tanning, etc.