In practical applications, most metals and ceramic materials are used in polycrystalline form, composed of numbers of tiny single crystals called grains.The atomic arrangements at the interfaces between these grains, namely the grain boundaries (GBs), are very different from those inside the bulk part.The GB atomic structures are rather complicated and disordered, dependent on the orientations between two adjacent grains.These GBs are generally thought to be detrimental to material properties;however, recent studies have shown that they can be beneficial, and sometimes even exhibit completely different mechanical [1], electrical [2,3] and chemical properties [4,5].In a research article published recently in NSR, Li and coauthors presented a new story of GB functionality, with a report of spin-valve magnetoresistance at a SrRuO3 (SRO) GB [6].