The recent emergence of 2D van der Waals magnets down to atomic layer thickness provides an exciting platform for exploring quantum magnetism and spintronics applications. The van der Waals nature stabilizes the long-range ferromagnetic order as a result of magnetic anisotropy. Furthermore, giant tunneling magnetoresistance and electrical control of magnetism have been reported. However, the potential of 2D van der Waals magnets for magnonics, magnon-based spintronics, has not been explored yet. Here, we report the experimental observation of long-distance magnon transport in quasi-twodimensional van der Waals antiferromagnet MnPS3, which demonstrates the 2D magnets as promising material candidates for magnonics. As the 2D MnPS3 thickness decreases, a shorter magnon diffusion length is observed, which could be attributed to the surface-impurity-induced magnon scattering. Our results could pave the way for exploring quantum magnonics phenomena and designing future magnonics devices based on 2D van der Waals magnets. I. INTRODUCTIONThe recent emergence of two-dimensional (2D) van der Waals magnets down to atomic-layer thickness has attracted considerable interest and provided an exciting platform for exploring new physical phenomena in low-dimensional magnetism [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The long-range ferromagnetic order in 2D magnets has been demonstrated in bilayer Cr2Ge2Te6 and single layer CrI3 as a result of magnetic anisotropy [1,2,16]. Shortly, the potential of such van der Waals ferromagnets for spintronics applications has been intensively explored. For example, giant tunneling magnetoresistance in bilayer CrI3 has been demonstrated [17][18][19], which is much higher compared to conventional single-crystalline-MgO barrier based ferromagnetic tunneling junctions [20,21].The important role of magnon-assistant tunneling through thin CrBr3 barriers has been shown in the graphene/CrBr3/graphene heterostructures [22]. Because of their 2D nature, efficient electrical control of magnetism in 2D ferromagnetic materials has also been explored [3,[23][24][25][26], which provides an alternative route towards high-temperature ferromagnetic semiconductors [27,28]. Furthermore, room-temperature 2D ferromagnetism in monolayer van der Waals magnet has also been demonstrated in epitaxial films and ionic liquid gated flakes [8,9,25].Magnonics refers to the magnon-based spintronics, the use of magnon-mediated spin current for information logic and computing applications [29]. One of the major research directions is to search the suitable magnon transport channel materials, which can propagate magnons over a long Sciences (Grant No. XDB28020100). References:[1]C.