By a simple hydrothermal method, a phase boundary between α- and β-Ni(OH)2 can be obtained. The Fenton-like performance of α@β-Ni(OH)2 is 1.56 times higher than that of single β-Ni(OH). α@β-Ni(OH)2 displays superior stability compared to α-Ni(OH)2, β-Ni(OH)2, and amorphous Ni(OH)2, which makes significant contributions to developing advanced catalysts in diverse fields.