With ammonium ions and 1,10-phenanthroline (phen) molecules as structure-directing agents, a new crystalline chalcogenide (NH₄)InSb₂S₅·phen (IAS) has been surfactant-thermally synthesized and fully characterized. The as-prepared IAS features a two dimensional (2D) layer structure with cationic ammonium and molecular phen located in the interlayers. Taking advantage of its unique structure and composition, IAS has been explored as an effective anode material for lithium/sodium ion batteries (LIBs/SIBs). IAS delivers a high capacity of 1107 mA h g⁻¹, a good rate stability up to 3.57 A g⁻¹ and an ultra-long stability as a superior anode for LIBs. The capacity retention could achieve a remarkably high value of 98% even after 1000 cycles of testing at 2.85 A g⁻¹. We also demonstrate SIBs utilizing IAS as the anode, which provides a capacity of 542 mA h g⁻¹ with a high coulombic efficiency (CE) of 96.35% at the 50^th cycle. These results indicate the ability of IAS to be deployed as an anode with good reversibility for future high performance LIBs/SIBs.