Meeting the need for materials with new properties sought in modern technologies, composites have found wide applications. With the advent of nanotechnology, a new window was opened in different scientific fields including composites science and nanocomposites were introduced. In these materials the superiority of material at nanometer scale over bulk state is exploited. Among nanocomposites those with polymer matrix reinforced by carbon nanotubes are of particular interest. In a novel form of these nanocomposites which has recently attracted attention, first a porous sheet composed of a random network of carbon nanotube bundles, called buckypaper, is made and then the composite is fabricated through infiltrating the resin into its pores. In the present research, firstly, necessarybasics including nanotechnology, properties of carbon element and its allotropes, composite, nanocomposite and modeling techniques were investigated. Then methods of fabrication of buckypaper including suspension filtration, frit compression, domino pushing, continuous production and hydroentangling, and vacuum assisted resin transfer molding and dipping methods for producing composites containing buckypaper sheets were studied. Then using an approach called molecular structural mechanics along with finite element method (ANSYS package), mechanical models were developed for graphene, single walled carbon nanotubes, multi walled carbon nanotubes, nanotube bundles, buckypaper and buckypaper/epoxy nanocomposite. In each step, the geometry of the model was generated by MATLAB programming and then was transferred to ANSYS as an APDL input file. Utilizing the models, elastic behavior of the mentioned nanostructures was simulatedandtheirelastic moduli were obtained. Effect of different parameters like diameter and chirality of carbon nanotubes, number of nanotubes in bundles, porosity of buckypaper and alignment of bundles in buckypaper nanocomposite wasinvestigated. The obtained results for carbon nanotubes are well close to the known values of about 1000 GPa for Young’s modulus and 500 GPa for shear modulus. Also, comparison between the obtained results for buckypaper and its nanocomposite and values reported in other theoretical and experimental researches (Young’s modulus of buckypaper 0.2-12.2 GPa and Young’s modulus of buckypaper nanocomposite 5-45 GPa) shows good agreement and implies the efficiency of the applied modeling approach. Results approve the idea of producing nanocomposite from buckypaper because the properties of nanocomposite show improvement over both buckypaper and epoxy in such a way that the improvement is six times the properties of the neat resin in some cases. Key Words : carbon nanotube, buckypaper, nanocomposite, modeling, mechanical properties, molecular structural mechanics, finite element method.