The application of the nano-sized materials continues to grow at a rapid rate in the fields of medicine, biotechnology, and environmental technology. Voltage-gated potassium currents play a key role in excitable cellular viability and function, especially in the central nervous system. The aim of this study was to investigate the actions of silver nano-particles (nano-Ag) on voltage-activated potassium currents in hippocampal CA1 neurons using whole cell patch-clamp technique. The hydrodynamic mean diameter of nano-Ag (10(-5) g mL(-1) ) was 223.9 nm in artificial cerebrospinal fluid (ACSF). Both types, transient potassium (I(A) ) and delayed rectifier potassium (I(K) ) current amplitudes were inhibited by the nano-Ag (10(-5) g mL(-1) ). The nano-Ag particles produced a hyperpolarizing shift in the activation-voltage curve of I(K) and inactivation-voltage curve of I(A) and also delayed the recovery of I(A) from inactivation. The results suggest that nano-Ag may have potential to alter the excitability of neurons by depressing the potassium channels.