Complexes of vanadium(IV) with aminopolycarboxylic acids, nitrilotriacetic (NTA), nitrilodiaceticpropionic (NDAP), nitrilodipropionicacetic (NDPA), and nitrilotripropionic (NTP) acids were studied by electromotrice force measurements [emf(H)] in 3.0M KCl ionic medium at 25 C. Data analysis using the least-squares program LETAGROP, according to the general reaction p Hþþq VO2þþr C3 !Hp(VO)qCr pþ2q 3r, indicates that the following complexes are formed (H3C ligands): NTA ([VOC] and [OHVOC]2 ); NDAP ([VOC] and [OHVOC]2 ); NDPA ([VOC] and [OHVOC]2 ); and NTP ([H2VOC]þ, HVOC, [VOC] , and [OHVOC]2 ). The following order of coordination capacity NTA4NDAP4NDPA4NTP is suggested, based on values of stability constants and is attributed to the increase in propionic groups in the sequence. The study confirms that five-membered ring chelates are the most stable for VIV, like CuII, NiII, lanthanides, and other heavier elements.