In the investigation of the extraction system of metals with 2, 4, 6-tris (2'-pyridyl) -s-triazine (TPTZ), it is often necessary to determine the amounts of the participating TPTZ in both aqueous and organic phases. A selective determination of TPTZ was established by the following procedure : Transfer a sample solution containing TPTZ {(0.21.2)mg} in a 50 cm3 measuring flask. Add 2 cm³ of 0.01 mol dm^-3 Mohr's salt solution and 1 cm³ of 10% hydroxylamine hydrochloride solution. Adjust the pH to 45 with acetate buffer solution, dilute to the mark with water, and measure the absorbance at 595 nm against, the reagent blank. In the ordinary extraction system involving TPTZ, the two phases were separated from each other and then the amounts of TPTZ in the aqueous phase was first determined as above. On the other hand, the organic phase was shaken with 6 mol dm^-3 hydrochloric acid to strip TPTZ. The amounts of TPTZ in the hydrochloric acid solution was determined. From the above two determinations, the percentage extraction of TPTZ was obtained with various organic solvents as a function pH of the aqueous phase. The pH_1/2 of TPTZ was found to be 0.38 with phenylcarbinol, 1.20 with chloroform, 1.72 with 1-butanol, 1.93 with nitrobenzene, 2.16 with dichloroethane, 2.28 with 1-pentanol, and 2.50 with trichloroethane.