Abstract: Guanethidine(Ⅰ),a new hypotensive agent,differs from older ones in that it blocks the transmission of the sympathetic nervous system by depleting stored catecholamines,but has no effects on the parasympathetic system. Pempidinc(Ⅱ)is a potent and longacting ganglionic blocking agent with proven clinical efficacy in the treatment of hypertension.It appears interesting to replace the heptamethylenimino group of guanethidine by the 2,2,6,6,-tetramethylpiperidino group of pempidine or by other α-methyl-substituted piperldines. The β-(α-methyl-substituted piperidino) ethylguanidine sulphates (Ⅲ_a,b,c) were prepared by the interaction of the appropriate β-(α-methyl-substituted piperidino)ethylamines and aqueous 2-methyl-2-thiopseudourea sulphate. The intermediate β-(α-methyl-substituted piperidino) ethylamines (Ⅶ_a,b,c) were in turn synthesized by condensation of α-methyl-substituted piperidines with chloroacetonitrile,and subsequent reduction of the nitriles so formed with lithium aluminium hydride. The hypotensive activities of these compounds were evaluated in anaesthetized dogs, cats, rats, and renal hypertensive dogs. Most compounds listed in Tables 2 and 3 were found to have hypotensive action.BD-31(Ⅲ_a) was the most active.It was fast in onset and its action lasted for 2—4 hours following single intravenous dose of 0.5—1.0 mg/kg.The compound has been sent for clinical trials.