The rapid development of zero-dimensional quantum dots-based nanotechnology has motivated the design and synthesis of novel nano-functional materials for optoelectronic and photonic devices in recent years. Antimony sulfide (Sb 2 S 3 ) quantum dots (SQDs), with an average diameter of 3.22 nm, were prepared via a top-down liquid ultrasonication exfoliation technique. Highly soluble poly( N -vinylcarbazole)-covalently functionalized SQDs (SQDs-PVK) were synthesized in situ by reversible addition fragmentation chain transfer polymerization, and embedded into a non-optically active poly(methylmethacrylate) (PMMA) matrix giving the SQDs-PVK/PMMA film. The annealed SQDs-PVK/PMMA film showed exceptional nonlinear optical performance, with large nonlinear absorption coefficients of 713.71 cm GW -1 at 532 nm and 913.60 cm GW -1 at 1064 nm, and small limiting thresholds of 1.44 J cm -2 at 532 nm and 1.08 J cm -2 at 1064 nm. These advantages make SQDs-PVK one of the promising candidates for a broadband optical limiter in both the near-infrared and visible ranges.