Polymethylmethacrylate/cellulose nanocomposites were prepared by in situ polymerization and ex situ dispersion techniques with 10 wt% loading of cellulose nanoparticles. Cellulose nanoparticles were prepared from jute fibers by acid hydrolysis. The suspension polymerization of methylmethacrylate was carried out in presence of cellulose nanoparticles, which were dispersed in water medium and in situ polymethylmethacrylate/cellulose nanocomposite granules were formed. These granules were dissolved in chloroform, sonicated and films were prepared by solution casting method (IPC). Polymethylmethacrylate granules were prepared by similar suspension polymerization process and made into films by solution casting method. Another set of polymethylmethacrylate/cellulose nanocomposite films were prepared by dispersing nanocellulose powder (10 wt%) in polymethylmethacrylate solution and casting into films (EPC). The unreinforced polymethylmethacrylate and polymethylmethacrylate extracted from IPC films were subjected to size exclusion chromatography and nuclear magnetic resonance study. The average molecular weights of neat polymethylmethacrylate and polymethylmethacrylate from IPC were quite close, but the 'dispersity' was slightly higher in IPC than that in neat polymethylmethacrylate. Fourier transform infrared spectroscopy revealed some shifts in EPC. X-ray diffraction study showed a similar nature of X-ray diffraction curves in all the samples. Transmission electron microscopy of IPC and EPC showed a better dispersion of fillers and formation of a network structure in IPC, whereas in EPC, the fillers were agglomerated. Surface morphology of the films was examined by field emission scanning electron microscopy and atomic force microscopy. IPC exhibited a much smoother surface compared to that of EPC indicating a more homogeneous dispersion of fillers. IPC showed a higher modulus of elasticity compared to PMMA and EPC. Differential scanning calorimetry showed a shift of glass transition temperature to a higher one (125 C) in IPC compared to that of polymethylmethacrylate (118 C). Thermogravimetric analysis was done to study the thermal degradation behavior of the composites. © The Author(s) 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.