The complexing behavior of poly(ethyleneimine) 5-sulfonyl-8-hydroxyquinoline (POX) with palladium(II) ions in aqueous solution was studied by means of spectrophotometry in the visible region. It was shown that poly(ethyleneimine) 5-sulfonyl-8-hydroxyquinoline forms a stable, water-soluble, orange-colored complex which has a maximum absorption at a wavelength of 424 nm. The effect of pH, concentration of poly(ethyleneimine) 5-sulfonyl-8-hydroxyquinoline, concentration of palladium(II) ions, and time were investigated. The results show that in a pH range between 2 and 5, the absorbance is constant for 40 minutes. The linear concentration range for palladium(II) ions was determined to be 0-2.5 μg · ml -1 and the molar extinction coefficients 1.06 · 10 4 (1 · mol -1 · cm -1 ) for the polymeric derivative and 7.15 · 10 3 for the monomeric 8-hydroxyquinoline. The effect of tartaric acid as a masking agent was examined in order to eliminate the influence from other ions. The simultaneous presence of K(I), Cs(I), Li(I), Ba(II), Ca(II), Cd(II), Hg(II), Mn(II), Ni(II), Al(III), As(III), Au(III), Cr(III), Fe(III), Pt(IV), As(V) did not interfere with the complexation of poly(ethyleneimine) 5-sulfonyl-8-hydroxyquinoline and palladium(II). However, it was found that NH 4 + interferes strongly. The polymer 8-hydroxyquinoline derivative exhibited a 45% higher sensitivity to Pd(II) ions in comparison to the low-molecular-weight 8-hydroxyquinoline.