As a specific digital holographic microscopy system, optical scanning holography (OSH) is an appealing technique that makes use of the advantages of holography in the application of optical microscopy. In OSH system, a three-dimensional object is scanned with a Fresnel zone plate in a raster fashion, and the electrical signals are demodulated into a complex hologram by heterodyne detection. Then the recorded light wavefront information contained in the hologram allows one to digitally reconstruct the specimen for multiple purposes such as optical sectioning, extended focused imaging as well as three-dimensional imaging. According to Abbe criterion, however, akin to those conventional microscopic imaging systems, OSH suffers from limited resolving power due to the finite sizes of the objective lens and the aperture, i.e., low numerical aperture. To bypass the diffraction barrier in light microscopy, various super-resolution imaging techniques have been proposed. Among those methods, structured illumination is an ensemble imaging concept that modulates the spatial frequency by projecting additional well-defined patterns with different orientation and phase shift onto the specimen. Computational algorithms are then applied to remove the effect of the structure and to reconstruct a super-resolved image beyond the diffraction-limit. In this paper, we introduce this technique in OSH system to scale down the spatial resolution beyond the diffraction limit. The performance of the proposed method is validated by simulation and experimental results.