We investigated the optimal manufacturing conditions of multi-walled carbon nanotubes(MWCNTs)/epoxy composite strain sensor in order to improve a sensitivity of the sensor. The specimens were manufactured and the electrical properties of the specimens compared according to different MWCNTs concentrations, dispersion methods, time, and the kind of solvents. The sensitivity of MWNTs/epoxy composite strain sensor was investigated quantitatively by measuring resistance changes according to the variation of a constant strain. Scanning electron microscopy (SEM) images confirmed that MWCNTs/epoxy composites with different CNT concentrations have a good homogeneity and dispersion. In addition, we attempted to evaluate the sensing characteristics and compared those of a conventional foil strain gauge. A MWCNTs/epoxy composite was attached to a host structure with facile processing. The response of MWCNTs/epoxy sensor was fairly good and the result was nearly identical to the strain gauge. And the dynamic response of the MWCNTs/epoxy was investigated to verify the feasibility of a damage detection sensor. In order to measure the dynamic response, a Wheatstone bridge circuit and a signal conditioning circuit were used. Also, this paper described the effect of MWCNTs agglomeration on the piezoresistivity of CNT-polymer composites. A 3-dimensional dispersion modeling using CNT percolating networks and tunneling effect has been developed, where the CNT agglomerates were modeled as randomly dispersed state in the polymer matrix. The newly developed model agrees quantitatively with experimental data. The current study on the sensitivity of MWCNTs/epoxy composite sensor provides a useful tool to design smart sensing and multi-functional polymer composites. The concept of using these conductive fillers provides a low-cost and effective way to fabricate piezoresistive polymer nano composites toward structural health monitoring applications.