Two photon polymerization, based on two-photon absorption, is a powerful and potential technique to fabricate 3D micro/nanostructures with submicrometric resolution. We use a photopolymerizable resin based on methyl methacrylate monomers as a photosensitive medium, in which the polymerization is triggered by the nonlinear optical effect. Nonlinear effect photoreaction occurs only in a submicrometric volume, voxel, much smaller than the cube of the wavelength, λ3. By using a femtosecond laser, 780 nm wavelength, we investigate the effect of different parameters on the resolution of our custom made micro/nanofabrication set up. The fabrication accuracy and the resolution of 3D micro/nanostructures depend on the accuracy of the focal spot position in z-direction, in the glass substrate-resin interface. We control the focal spot position by using ascending scan process meaning the focus spot level. Employing the proposed process, the lateral resolution of individual voxels, is improved almost to 94 nm. The resolution of two photon absorption polymerized voxels is studied as a function of focus spot level, laser power and single-shot irradiation time. Finally, we show 3D microstructures and a micro-device, which present great potential for future applications.