Basicity study of25,27-{2,2'-[2,2'-((2,5,8-triaza)nonyl)diphenoxy]diethyl}-p-tertbutylcalix[4]arene(L) and stability of its complexes with transitionmetal ions (M2+), including Co2+, Ni2+, Cu2+ and Zn2+were investigated at 25 degree C by potentiometrictitration method. Three protonation constants of theligand L, in the methanolic solution of 5.0 x 10('-2) MEt4NCI0(,4) and 5.0 x 10('-2) M Bu4NCF3SO3 wereobtained. The three protonation constants in themethanolic solution of 5.0 x 10-2 M Et4NCI04 werelarger than those in the methanolic solution of 5.0 x10-2 M Bu4NCF3SO3. The order of magnitude of thestability of the ligand L complexes with the Co2+,Ni2+, Cu2+ and Zn2+ in the methanolic solution of 5.0 x10-2 M Bu4NCF3SO3 found as ML2+ species, decreases fromCu2+ > Ni2+ > Co2+ > Zn2+. The complex species with theCu2+ and Zn2+ were formed as CuL(OCH3)+ and Zn2L4+respectively.