Pure samples of Na2TeS3 and Na2TeSe3 were synthesized by the reactions of stoichiometric amounts of the elements Na, Te, and Q (Q = S, Se) in the ratio 2:1:3. Both compounds are highly air- and moisture-sensitive. The crystal structures were determined by single-crystal X-ray diffraction. Yellow Na2TeS3 crystallizes in the space group P2(1)/c. Na2TeS3 exists in a low-temperature modification (Na2TeSe3-mP24, space group P2(1)/c) and a high-temperature modification (Na2TeS3-mC48, space group C2/c); both modifications are red. Density functional theory calculations confirmed the coexistence of both modifications of Na2TeS3 because they are very close in energy (Delta E = 0.18 kJ mol(-1)). To the contrary, hypothetic Na2TeS3-mC48 is significantly less favored (Delta E = 1.8 kJ mol(-1)) than the primitive modification. Na2TeS3 and Na2TeS3-mP24 are isotypic to Li2TeS3, whereas Na2TeS3-mC48 crystallizes in its own structure type, which was first described by Eisenmann and Zagler. The title compounds have two common structure motifs. Trigonal TeQ(3) pyramids form layers, and the Na atoms are surrounded by a distorted octahedral environment of chalcogen atoms. Raman spectra are dominated by the vibration modes of the TeQ(3) units. The activation energies of the total conductivity of the title compounds range between 0.68 eV (Na2TeS3) and 1.1 eV (Na2TeS3). Direct principal band gaps of 1.20 and 1.72 eV were calculated for Na2TeS3 and Na2TeS3, respectively. The optical band gaps are in the range from 1.38 eV for Li(2)TeSe3 to 2.35 eV for Na2TeS3.