Ternary sulfide NaSbS2 is a low-cost, environment-friendly semiconductor that has rarely been studied. This paper demonstrates, for the first time, solid-state NaSbS2 quantum dot-sensitized solar cells (QDSSCs). NaSbS2 nanoparticles were synthesized using the sequential ionic layer adsorption reaction method. Solid-state QDSSCs were fabricated from the synthesized nanoparticles using spiro-OMeTAD as the hole-transporting electrolyte. The best cell yielded an efficiency of 1.27% under 1 sun. At the reduced light intensity I 0 of 10% sun, the efficiency increased significantly to 4.11% with an open-circuit voltage $V_{{\text{oc}}}$ of 0.51 V, a short-circuit current density J sc of 1.68 mA/cm2, and a fill factor (FF) of 47.8%. A sublinear power law of J sc∝ I 0 0.52 accounts for the large improvement in performance under low-light intensities because of the reduced carrier recombination. The external quantum efficiency (EQE) spectrum covered the spectral region of 300–750 nm with a maximum EQE value of 72% at λ = 450 nm. The present efficiency (4.11%) represents about 30% improvement over the best previous result (3.18%) of liquid-junction QDSSCs. The respectable efficiency indicates that NaSbS2 shows potential as an efficient solar absorber material.