The six LnYb Q 3 compounds β-LaYbS 3, LaYbSe 3, CeYbSe 3, PrYbSe 3, NdYbSe 3, and SmYbSe 3 have been synthesized from high-temperature solid-state reactions of the constituent elements at 1223 K. The compounds are isostructural to UFeS 3 and crystallize in the space group Cmcm of the orthorhombic system with four formula units in a cell. Cell constants (Å) at 153 K are: β-LaYbS 3, 3.9238(8), 12.632(3), 9.514(2); LaYbSe 3, 4.0616(8), 13.094(3), 9.932(2); CeYbSe 3, 4.0234(5), 13.065(2), 9.885(1); PrYbSe 3, 4.0152(5), 13.053(2), 9.868(1); NdYbSe 3, 4.0015(6), 13.047(2), 9.859(1); SmYbSe 3, 3.9780(9), 13.040(3), 9.860(2). The structure is composed of layers of Yb Q 6 ( Q=S or Se) octahedra that alternate with layers of LnQ 8 bicapped trigonal prisms along the b-axis. Because there are no Q– Q bonds in the structure the formal oxidation states of Ln/Yb/ Q are 3+/3+/2−. Magnetic susceptibility measurements indicate that CeYbSe 3 and SmYbSe 3 are Curie–Weiss paramagnets over the temperature range 5–300 K.