Electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) were performed to investigate the difference in microenvironments and functions between tyrosine Z (Y_Z) and tyrosine D (Y_D). Mn-depletion or Ca²⁺-depletion causes extension of the lifetime of tyrosine radical Y_Z ^•, which can be trapped by rapid freezing after illumination at about 250 K. Above pH 6.5, Y_Z ^• radical in Mn-depleted PS II shows similar EPR and ENDOR spectra similar to that of Y_D ^• radical, which are ascribed to a typical neutral tyrosine radical. Below pH 6.5, Y_Z ^• radical shows quite different EPR and ENDOR spectra. ENDOR spectra show the spin density distribution of the low-pH form of Y_Z ^• that has been quite different from the high-pH form of Y_Z ^•. The spin density distribution of the low-pH Y_Z ^• can be explained by a cation radical or the neutral radical induced by strong electrostatic interaction. The pH dependence of the activation energy of the recombination rate between Y_Z ^• and Q_A ⁻ shows a gap of 4.4 kJ/mol at pH 6.0–6.5. In the Ca²⁺-depleted PS II, Y_Z ^• signal was the mixture of the cation-like and normal neutral radicals, and the pH dependence of Y_Z ^• spectrum in Ca²⁺-depleted PS II is considerably different from the neutral radical found in Mn-depleted PS II. Based on the recent structure data of cyanobacterial PS II, the pH dependence of Y_Z ^• could be ascribed to the modification of the local structure and hydrogen-bonding network induced by the dissociation of ASP170 near Y_Z.