Since the usefulness of o-caxboxymethyhnercaptobenzenestibonic acid (Ⅱ) against trypanosomiasis, trichomoniasis and leishmaniasis was announced^[2], its m-(Ⅲ) and p-isomem (Ⅳa) have been prepared in our laboratory. The latter compound (Ⅳa) was found to be more active than tartar emetic against schis-tosomiasis japonica in a long course treatment in mice}g}. In order to eeamine the relationship between the chemical structure and the pharmacological activity, the corresponding ester (Ⅳb), amide (Ⅳc), alcohol (Ⅳd) and sulphone (Ⅳe) were then prepared.