Reaction–diffusion (RD) processes are responsible for surface and in-depth micropatterning in inanimate and living matter. Here we show that enzyme-assisted self-assembly (EASA) of peptides is a valuable tool to functionnalize host gels. By using a phosphatase distributed in a host hydrogel, the diffusion of phosphorylated peptides from a liquid/host gel interface leads to the spontaneous formation of a pattern of dephosphorylated peptide self-assembly presenting at least two self-assembly maxima. Variation of enzyme and peptide concentrations change the pattern characteristics. When a peptide drop is deposited on a phosphatase functionalized gel, a self-assembly pattern is also formed both along the gel-solution interface and perpendicular to the interface. This self-assembly pattern induces a local change of the gel mechanical properties measured by nanoindentation. Its appearance relies on the formation of self-assembled structures by nucleation and growth processes which are static in the hydrogel. This process presents great similarities with the Liesegang pattern formation and must be taken into account for the functionalization of hydrogels by EASA. A mechanism based on RD is proposed leading to an effective mathematical model accounting for the pattern formation. This work highlights EASA as a tool to design organic Liesegang-like microstructured materials with potential applications in biomaterials and artificial living systems design.