A quasi-two-dimensional manganese-based compound ThMnSbN was synthesized by the solid-state reaction method. Structural refinement based on X-ray powder diffraction shows that the compound belongs to the P4/nmm space group. The lattice parameters are a=4.1731 ?, c=9.5160 ?. Electrical transport measurements show that the resistivity of the compound is one of the lowest among the Mn-based family. Upon cooling, the resistivity rises slowly and shows a shoulder-like anomaly at 16 K. Also, the magnetic susceptibility exhibits an anomaly at the very same temperature. Though the transition-induced anomaly is absent on the specific heat data, the electron specific heat coefficient of γ=19.7 mJ/mol/K2 is derived by fitting the low-temperature C-T curve. This γ value is much higher than those of the isostructural manganese-based compounds. Thus, the specific heat is consistent with the low resistivity and suggests a considerable electronic density of states near the Fermi surface for ThMnSbN. By comparing the crystal structure for a group of ZrCuSiAs-type compounds, various chemical pressure effects of the fluorite-type Th2N2 layer on the conducting layer in different compounds are discussed.