a modular columbarium system comprised of modular niche units each having a plurality of urn niches defined therein , wherein adjacent modular niche units are secured to one utilizing an interlocking system that provides alignment and stabilization of the units . the columbarium system is a modular design which facilitates the easy relocation of the modular niche units and the redesign of the columbarium system . the interlocking system connects the modules of the columbarium system to one another to enable easy expansion of the system without diminishing its stability . the modular niche units can also be used with existing columbarium systems . memorial plates of various sizes are provided to cover the niche openings such that couples or family members can be grouped together under one memorial plate .