The magnetic field effect on oscillating motion and heat transfer in an oscillating heat pipe (OHP) containing magnetic nanofluid was investigated experimentally. The nanofluid consisted of distilled water and dysprosium (III) oxide nanoparticles with an average size of 98 nm. A magnetic field was applied to the evaporating section of the OHP by using a permanent magnet. The heat pipes charged with magnetic nanofluids at mass ratios of 0.1%, 0.05%, and 0.01% were tested. In addition, the effects of orientation and input power ranging from 50 W to 250 W on the heat transport capability of the heat pipe were investigated. The experimental results demonstrate that the magnetic field can affect the oscillating motions and enhance the heat transfer performance of the magnetic nanofluid OHP. The magnetic nanoparticles in a magnetic field can reduce the startup power of oscillating motion and enhance the heat transfer performance.