Diatoms are unicellular photosynthetic algae enclosed in 3-dimensional (3D) nano patterned silica cell walls called frustules. They are made of intricate porous biosilica that feature unique properties including high specific surface area, biocompatibility, tailorable surface chemistry, thermal stability and high mechanical and chemical resistance. Additionally, the facile cultivation of diatoms in artificial environment, and the abundant availability of diatom frustules as fossilized mineral (diatomite) from mining industry confirm the benefits of using diatoms as an alternative to synthetic porous silica for a broad range of applications. These attributes make them a remarkable candidate for a variety of biomedical applications including drug delivery. In this chapter, the potential use of diatoms, as micro- and nano frustules (i.e., silica) or reduced to silicon replicas, for biomedical applications with emphasis on their use as drug carriers is described. The selected aspects on the preparation of diatom frustules, in addition to surface chemical functionalization, drug loading, their cellular uptake as well as capability to transport therapeutic molecules inside cells are presented