In this paper we present a method for tomographic imaging using multiple wavelengths in digital holographic microscopy. This method is based on the recording at different wavelengths equally separated in the k-domain, in off- axis geometry of the interference between a reference wave and an object wave reflected by a microscopic sample and magnified by a microscope objective. A couple charged device (CCD) camera records consecutively the resulting holograms, which are then numerically reconstructed to obtain their resulting wavefront. Those wavefronts are then summed. The result of this operation is a constructive addition of complex waves in the selected plane and destructive addition in the others. Varying the plane of interest enables the scan the object in depth. For the presented simulations and experiments, twenty wavelengths are used in the 480-700 nm range. An object consisting of irregularly stairs with heights of 375, 525, 975, 1200 and 1275 run is reconstructed. Its lateral dimensions are 250 x 250 microns. The results show clearly a 3D imaging technique with axial resolution under the micron.