Two dimensional (2D) MoS₂ nanosheets are firstly exfoliated by high shear mixing technique and then incorporated into PAA precursors to form the MoS₂/PI nanocomposite films, and the preparation can be accomplished via in-situ polymerization, tape casting and thermal imidization processes. As a result, the mechanical and thermal properties of the prepared MoS₂/PI nanocomposite films are significantly enhanced by incorporation of a small amount of MoS₂ nanosheets without any surface modification. Especially, 43% and 47% increases in tensile strength and Young’s modulus can be respectively achieved upon adding certain small amount of MoS₂ (0.75 wt% or so). Meanwhile, the glass transition temperature (T_g) can be effectively improved by 11 °C by taking advantages of unique superior thermal stability of MoS₂ nanosheets. This desirable fabrication of MoS₂/PI nanocomposite films is expected to offer a new avenue on the development of high strength PI-based nanocomposites with comprehensive performances.