Photo‐responsive lanthanide‐based single‐molecule magnets (SMM) hold great promise for future switching and memory devices. Herein, we report a dysprosium phosphonate DyIII(SCN)2(NO3)(depma)2(4‐hpy)2 (1Dy), which features a supramolecular framework containing layers of hydrogen‐bonding network and pillars of π–π interacted anthracene units. The photocycloaddition reaction of anthracene pairs led to a rapid and reversible single‐crystal‐to‐single‐crystal (SC–SC) structural transition to form the 1D coordination polymer DyIII(SCN)2(NO3)(depma2)(4‐hpy)2n (2Dy), accompanied by photoswitchable SMM properties with the reduction of effective energy barrier by half and the narrowing of the butterfly‐like hysteresis loop. The diluted sample showed a photo‐induced switch of the blocking temperature (TB) from 3.8 K for 1Dy@Y to 2.6 K for 2Dy@Y. This work may inspire the construction of lanthanide‐based molecular materials with targeted photo‐responsive magnetic properties. A reversible photo‐induced single‐crystal‐to‐single‐crystal structural transformation was achieved for a mononuclear dysprosium‐anthracene compound to form a 1D coordination polymer. This compound displays photoswitchable SMM properties with reduced effective spin‐reversal energy barrier, narrowed butterfly‐like hysteresis loop, and decreased blocking temperature.