Abstract The role of surface states in the photoelectrochemistry of phthalocyaninatozinc(II) (PcZn) has been investigated by time-resolved photocurrent measurements in the millisecond range and by photovoltage measurements. Plots of the photovoltage against the redox potential of the electrolyte yielded slopes a with −1 a 0 indicating partial Fermi-level pinning due to the presence of surface states. The charging and discharging of the surface states could be seen clearly in the photocurrent transients. The amount of charging and discharging was found to be determined by the recombination rate as a function of the applied electrode potential and by the charge–transfer rate, which was studied in dependence upon the nature and the concentration of the redox couple in the electrolyte (ferri/ferrocyanide, hydroquinone/benzoquinone) in comparison to oxygen- saturated and deaerated KCl electrolytes. The charge–transfer rate was found to be limited by an adsorption step of the electroactive species. The number of surface states was found to increase with exposure to air. This is interpreted as a modification of the PcZn surface due to reaction with oxygen. The surface state densities as derived from the extent of the Fermi-level pinning corresponded well with the discharges seen in the photocurrent transients and show that a considerable fraction of the PcZn surface molecules represents surface states after longer exposure to air.