The invention relates to the use of at least one sulfur-containing amino acid for stabilizing recycled thermoplastics, in particular against oxidative, thermal, and/or actinic degradation, to a recycled thermoplastic composition containing or consisting of at least one recycled thermoplastic and at least one sulfur-containing amino acid, to a molded part which can be produced from the recycled thermoplastic composition according to the invention, to a stabilizer composition, to a masterbatch, and to a stabilizing method, in particular an oxidative, thermal, and/or actinic stabilizing method for stabilizing recycled thermoplastics by adding or incorporating at least one sulfur-containing amino acid, a stabilizer composition according to the invention, or a masterbatch according to the invention to a recycled thermoplastic.