This study investigated the e_ect of temperature and time at temperatures lower than 0℃ on mortar mixed with antifreezing admixture to determine the temperature–time function with the aim of expressing the e_ect universally. As a result, the maturity equation for temperatures lower than 0℃ proposed in previous studies was verified to be applicable to type-B blast furnace slag cement. The applicability of this equation at temperatures lower than 0℃ had not been investigated hitherto. The strength development attributable to the e_ect of the antifreezing admixture can be expressed as the reference temperature, and the reduction in the chemical potential of water chemical potential reduction was found to depend on the reaction rate. A new maturity equation for temperatures lower than 0℃ was proposed considering the e_ect of the antifreezing admixture.