Metal sulfides are promising materials because their ability to capture radioactive nuclides from wastewater is superior to many others. Herein, Na/Zn/Sn/S (NaZTS) quaternary metal sulfide nanosheets were fabricated using a one-pot hydrothermal method. A series of characterizations revealed that these nanosheets had a structure identical to Na5Zn3.5Sn3.5S13·6H2O, consisting of [Zn3.5Sn3.5S13]5− frameworks and Na+ ions located at the center and corner of the open channels. Because of the S2− ligands in its structure, NaZTS was a soft Lewis base and showed high affinity toward Sr2+ ions. NaZTS was employed to remove Sr2+ from aqueous solutions and exhibited ultrafast kinetics (an equilibrium time of 5 min), a broad active pH range (a removal rate of >98.4% at pH 3–12), and a very low Sr2+ desorption rate of <0.04%. Its maximum adsorption capacity according to the Langmuir model was 40.4 mg g−1 at 318 K. The effects of adsorbent dosage and coexisting ions on Sr2+ adsorption were also discussed. Macroscopic adsorption experiments and microscopic X-ray photoelectron spectroscopy were used to study the adsorption mechanism, and the outstanding ability of NaZTS to capture Sr2+ ions could be attributed to ion exchange and strong Sr⋯S bonding. This work highlights the excellent adsorption of Sr2+ by NaZTS, which makes it a promising material for removing radioactive Sr2+ in cleanups of radioactive pollution.