The electrical conductivity of microemulsions composed of aerosol OT (AOT), isooctane, and water as a function of temperature was studied in the absence and presence of azobenzene, and consequences of an in situ trans-cis photoisomerization of azobenzene were investigated. A conductivity onset upon raising the temperature of a water-in-oil microemulsion indicates percolation. Small amounts (0.1-5% w/w) of solubilized azobenzene induce higher percolation temperatures T-p (by up to 19 K). and photoisomerization of azobenzene shifts T-p back to values that may be below T-p in the absence of azobenzene, Consequently, the microemulsion can be switched front nonconducting to conducting by exposing samples to UV-light at lambda > 310 nm, without varying temperature or composition. The effect reverts within several minutes after turning off the irradiation lamp through thermal reisomerization. By that, reversible switching of electrical conductivity is brought about.