In this study, the elastic modulus of 1 wt. % multiwalled carbon nanotube (MWCNT) reinforced epoxy composite was characterized using an in-house designed micro/nano tensile load stage in conjunction with an atomic force microscope (AFM). The surface of the nanocomposite was scanned by the AFM during intermittent tensile testing, and micro/nanoscale deformation was observed. The MWCNT reinforced nanocomposite exhibited a 23% increase in the measured elastic modulus compared with the pure epoxy. The elastic moduli of the nanocomposite were also predicted by the Halpin–Tsai and Hui–Shia models, and the former offered a better correlation with the experimental result when only the load bearing outer layer of the MWCNTs was considered. The combination of the load stage and AFM is capable of capturing the in situ deformation progress for small strain increments.