Light-matter interactions can be strongly modified by the surrounding environment.Here,we report on the first experimental observation of molecular spontaneous emission inside a highly non-local metamaterial based on a plasmonic nanomd assembly.We show that the emission process is dominated not only by the topology of its local effective medium dispersion,but also by the non-local response of the composite,so that metamaterials with different geometric parameters but the same local effective medium properties exhibit different Purcell factors.A record-high enhancement of a decay rate is observed,in agreement with the developed quantitative description of the Purcell effect in a non-local medium.An engineered material non-locality introduces an additional degree of freedom into quantum electmdynamics,enabling new applications in quantum information processing,photochemistry,imaging and sensing with macroscopic composites.