Optical second harmonic generation, thanks to its coherent nature, is a suitable signal for interferometric measurements, such as digital holography: a well-established imaging technique that allows recovering of the complex diffraction wavefields from which it is possible to extract both amplitude- contrast and quantitative phase images. We believe that application of digital holography to non-linear optical fields might ultimately be the key to phase- related functional imaging. In a first approach, we report here on second harmonic generation digital holographic microscopy, and present its application to (1) discrimination of nanoparticles of different nature - here polystyrene microspheres and barium titanate (BaTiO3) nanoparticles - and to (2) 3D-mapping of a distribution of BaTiO3 nanoparticles.