S-2, W-diaminopentyl isothiuronium bromide and relevant thiophosphate derivative were prepared starting from both phthalimide and l-ornithinic acid. Drug toxicities of the prepared isothiuronium bromide and S-2-(W-aminoalkylamino) ethyl isothiuronium bromides were tested through ICR male mice, 4 and 8 weeks old and weighing $25{sim}35g$. The former compound was found to be less toxic than those of latter compounds. This difference of drug toxicities seemed to be originated from their chemical structures, which were examined through IR Spectrometry Radioprotective effects of these compounds were discussed through relevant research data and diaminopentyl derivatives are considered to be a potent radioprotectant with low drug toxicity.