Abstract: In our early work, it was shown that p-chlorophenylethylamine and chloropromazine exhibited remarkable protective effect against ionization radiation in mice. The prophylactic mechanisms of these drugs were quite different from that of mercaptoethylamine. Accordingly, synthesis of compounds structurally related to both p-chlorophenylethylamine and chloropromazine would be interesting in search for antiradiation drugs.N-amino-alkyl-2-phenyl-thiomorpholine Ⅲ and some of its derivatives are structurally related to p-chlorophenylethylamine and chloropromzine since they may be regarded as the open ring analogs of chloropromazine and bear the phenylethylamine structure as well. They were synthesized in five steps starting from the corresponding α-bromophenylacetic acid ethyl esters. Among them Ⅲ_d showed protective activities against ionization radiation in mice.