The N-dichloroacetyl derivatives of DL-serine and DL-threonine were prepared by the Schotten–Baumann reaction from the amino acids and dichloroacetyl chloride. Negative ninhydrin tests coupled with elementary analyses indicated that only the amino group was acylated. The ester derivatives of these compounds were prepared either by esterification of the N-dichloroacetyl-DL-amino acid with diazomethane or by the reaction of the amino acid ester with dichloroacetyl chloride in the presence of triethylamine. The sodium salts and the esters were tested for antitumor activity against sarcoma 37 in mice and Walker carcinoma 256 in rats. In both cases regression of the tumors was obtained.