A new fluorescent probe based on terbium(III)-doped nanosheets was designed for detecting low-levels of dipicolinic acid (DPA), a biomarker of bacterial spores. The ability to detect ultra-low concentrations of DPA is therefore of great significance. First, Tb(III)-doped ytterbium hydroxide nanosheets were obtained by mechanical exfoliation from layered rare-earth hydroxide (LRH) materials. The morphology of the as-synthesized nanosheets was studied by transmission electron microscopy and atomic force microscopy. The Tb(III)-doped nanosheets are demonstrated to be highly sensitive to DPA, which remarkably enhances Tb(III) luminescence intensities at a wavelength of 544 nm. Furthermore, Tb(III) emission increases linearly with DPA concentration. Selectivity studies were conducted by adding different competing aromatic ligands to the sensing solution; however, their fluorescence responses were observed to be negligibly small in comparison with that of DPA. Our findings provide a basis for the application of Tb(III)-doped nanosheets for accurate, sensitive, and selective monitoring of DPA as a biomarker of anthrax.