The conditions of synthesis of ion associates of phosphorus-molybdenum ions with protonated form of lysine hydrochloride have been considered. It has been shown that the phosphoric molybdenum acid undergoes hydrolysis with the formation of the following products: НРО42– + Мо12О42– + 11Н2О. At pH 2 in aqueous solutions, the PhMA is stable, exists as anion [РМо12О42]3– and interacts with protonated form of lysine with the formation of associates 3[НLys]+[FMC]3–. The molar ratio of lysine: PhMA = 3 : 1 was proved by potentiometric titration, these molar ratios were confirmed by the data of elemental analysis, IR spectroscopic study of the obtained associate showed the presence of a fragment -Mo-O (? = 1900–500 cm–1) and a group –NH3– (? =3500–3650 cm–1), which indicates the ionic nature of the relationship between the PhMA anion and the lysine cation. The plasticized membrane was obtained by adding 0.050 g of dried associate 8 ml of cyclohexanone and 0.4316 g of dibutyl phthalate to the sample. Heated to 60° C and added with stirring in small portions 0.2522 g polyvinyl chloride. After dissolution of polyvinyl chloride, the finished transparent substance was placed into a Petri dish (d = 61 mm) and dried in the air for three days. Then, the ion-selective membrane was attached to the carefully polished end of the graphite rod, the diameter of which corresponded to the diameter of the tube (6–8 mm). After drying before work, the electrode was conditioned for 24 hours in a 10–3 M lysine solution. The electrode function is linear in the concentration range of 10–2–10–5 M. The morphology of phosphoric molybdenum acid and its associate with lysine was studied for the first time.