Jute yarn reinforced polypropylene commingled composites were prepared by an environmentally benign technique called commingling method in which the matrix fibres and reinforcing fibres are intermingled together with good alignment. The dynamic mechanical properties or viscoelastic behaviour of these commingled composites were studied with reference to fibre content and various chemical treatments. The storage and loss modulus increased with fibre content where as tan δ decreased. KMnO4 and MAPP treated composites showed much higher storage and loss modulus values at all temperatures compared to untreated one. The glass transition temperature showed a marginal increasing tendency with fibre content and chemical treatments. The surface treatment mechanisms were supported by FT-IR spectra and the increase in interfacial adhesion after chemical treatments were supported by SEM images. Theoretical modelling was used to predict the values of storage modulus and tan δ and was found to be comparable with that of experimentally obtained results.