Persistent photoconductivity is an interesting and unusual property of high Tc superconductors. Underdoped YBa2Cu3O6+δ shows upon illumination a decrease of resistivity and an increase of Tc. These photoinduced changes are persistent at low temperatures and relax at room temperatures. A possible model for persistent photoconductivity in these materials is that electrons of photoinduced electron-hole pairs are trapped at localized states spatially separated from the conduction layer. We recently measured persistent photoconductivity in Tl2Ba2CuO6+δ and Y-doped Bi2Sr2CaCu8+δ, which indicates that persistent photoconductivity might be a common phenomena in high-Tc superconductors.