This paper presents a theoretical analysis of the rheological behaviour of graphene-filled polystyrene nanocomposites using an existing FENE (finitely extensible non-linear elastic) model based on the stochastic differential equations. A series of these nanocomposites were prepared by in situ polymerization of styrene monomer. During polymerization, graphene was added and a number of composites were prepared by varying the percentage of graphene in the step of 0.25wt % Nanocomposite samples were hot pressed as discs and then characterised for their rheological behaviour. Experimentally, it was observed that rheological properties such as storage modulus (G′) loss modulus (G′′) and complex viscosity η∗ increased with increasing graphene weight percentage. Using the FENE model it was predicted that graphene as a filler either affected the extension of the springs or spring constant. Consequently, a larger force was required to deform which improved the rheological properties of the polymer nanocomposites.