Core-shell　MOF@MOF　structures　are　good　candidates　for　the　design　of　diverse　multifunctional　materials　with　intriguing　properties.　Conventional　seed-induced　growth　procedures　to　create　MOF@MOF　usually　suffer　from　limitations　including　the　unavoidable　nucleation/growth　of　the　shell　MOF　in　solution　and　the　inevitable　agglomeration　of　seeds.　For　the　first　time,　an　ion-modulation　(Fe3+　as　the　indicator)　strategy　is　demonstrated　to　realize　one-pot　synthesis　of　monodisperse　MOF@MOF　composed　of　two　distinct　Prussian　blue　analogues　(PBAs).　It　utilized　a　finite　amount　of　Fe3+　to　induce　a　partial　phase　transition　and　generate　new　PBA　nanoparticles　epitaxially　growing　on　the　original　PBA　core.　The　as-prepared　PBA@PBA　with　a　distinct　morphology,　readily　tunable　by　controlling　the　dose　of　dopant　ions,　can　serve　as　a　template　for　the　creation　of　PBA　nanocages　with　uncommon　and　tunable　shapes　for　efficient　phenol　scavenging.　The　findings　here　pave　the　way　for　the　rational　design　of　MOFs　with　high　complexity,　good　structural　flexibility,　and　desirable　activity.