Abstract: New soluble MoS₂ nanosheets covalently functionalized with polystyrene (PS), MoS₂-PS, was in situ synthesized. The open-aperture Z-scan results demonstrated that both the solution of MoS₂-PS in DMF and the MoS₂-PS/PMMA film showed superior nonlinear optical (NLO) and optical limiting (OL) responses when compared to MoS₂ and MoS₂/PS blends. The thin films had a much higher concentration than the solutions at the same level of linear transmission, resulting in a much larger β_eff. In particular, for the MoS₂-PS/PMMA film, β_eff were 407.70 cm/GW at 532 nm (100.69 cm/GW for MoS₂-PMMA and 116.55 cm/GW for MoS₂/PS/PMMA) and 429.64 cm/GW at 1 064 nm (-48.92 cm/GW for MoS₂-PMMA and 66.31 cm/GW for MoS₂/PS/PMMA). A larger OL effect, with thresholds of about 0.92 GW/cm² at 532 nm and about 1.12 GW/cm² at 1 064 nm, was also achieved from the MoS₂-PS/PMMA film. The annealing treatment on the MoS₂-PS film resulted in the considerable enhancement of its NLO and OL performance. The achieved β_eff and OL thresholds were 455.67 cm/GW at 532 nm and 448.90 cm/GW at 1 064 nm; and 1.07 GW/cm² at 532 nm and 0.87 GW/cm² at 1 064 nm, respectively.