Frequency and magnetic field dependent dielectric measurements have been performed on epitaxial thin films of the double perovskite La2 NiMn O6, revealing a dielectric relaxation and magnetodielectric effect. The films are grown on Nb-doped and SrRu O3 -coated SrTi O3 substrates using the pulsed laser deposition technique. While a rapid dielectric relaxation is observed at ∼300 K, the relaxation rate increases dramatically at lower temperatures. Below the Curie temperature of La2 NiMn O6, the dielectric constant increases in a magnetic field for a range of temperature. This temperature range depends on magnetic field and measurement frequency. The results are explained by the influence of a magnetic field on the dipolar relaxation. © 2008 American Institute of Physics.