The electrical conductivity and piezoresistivity of carbon nanotubes(CNTs) cement mortars with 020%(by mass) styrene butadiene rubber emulsion(SBR) added were experimentally studied. The microstructure of CNTs cement mortars with or without SBR was investigated by using scanning electron microscopy(SEM)，and action mechanism of SBR on the electrical conductivity and piezoresistivity of CNTs cement mortars was discussed. The results show that both the electrical conductivity and piezoresistivity of CNTs cement mortars increase with increasing use level of SBR, and the optimal use level of SBR is 15%. It is found that CNTs are uniformly dispersed in SBR, and SBR could seal pores and form a three dimensional polymer network. As a result, there are more CNTs conductive units, and the electrical conductivity and piezoresistivity of CNTs cement mortars are improved with increasing use level of SBR. However, when the use level of SBR is higher than 15%, because of SBRs film forming and air entraining action the porosity of the mortar increases，and relative concentration of CNTs in SBR CNTs system reduces duo to higher content of SBR, so that the number of CNTs conductive units decreases causing lower electrical conductivity and piezoresistivity of CNTs cement mortars.