The purpose of this study was to investigate the change in the physical and mechanical properties of styrene-butadiene copolymer (SB) dispersion-modified calcium sulfoaluminate (CSA) cement mortar as it aged from 28 to 360 d, and cured at different temperatures and relative humidities. The results show that the mechanical properties of reference mortar (RM) of CSA cement, including its flexural, compressive, and tensile bond strength, showed a reduction after a certain time, but its water ca-pillary absorption was hardly affected by age. When SB dispersion was added, there was no reduction in mechanical strength. The amount of SB added did matter. Addition of 5％ SB had a negative effect on most properties compared with RM, except for tensile bond strength. However, the properties of SB-modified mortar (SBMM) were enhanced significantly as the amount of SB was increased from 5％ to 20％. Temperature change had different effects on the properties of RM and SBMM. High temperature was beneficial to early flexural and compressive strength development of RM, but caused serious strength reduction at later stages. High temperature enhanced the development of tensile bond strength of RM. Increasing temperature enhanced properties of SBMM, including flexural, compressive, and tensile bond strength. Higher relative humidity improved all measured properties of all mortars. Scanning electron microscope (SEM) observations of the morphology of RM and SBMM at 360 d cured under dif-ferent conditions accounted well for the changes in mechanical properties.