The NaK 2 InSb 2 quaternary compound, which crystallizes in the orthorhombic structure with the lattice parameters a = 1403.2 ± 0.2, b = 1639.9 ± 0.3, and c = 700.9 ± 0.1 pm and a calculated density of 3.784 g·cm−3, is formed in the In–Na–K–Sb system (Carrillo-Cabrera et al. 1993). This compound was synthesized in sealed Nb ampoules from the stoichiometric mixture of elements, which were heated at 630°C for 2 days and then slowly cooled to room temperature (6°C·h−1). NaK2InSb2 forms platelike crystals with silver metallic luster, which are very unstable in air and moisture. The title compound begins to decompose at about 670°C in high vacuum.