Asphalt binder plays a critical role in defining the low-temperature performance of asphalt pavement, and, therefore, enhancing its mechanical behavior at low service temperatures through modification always has been of great interest. Crumb rubber modification of asphalt is one of the common practices in the industry. However, the effect of a crumb rubber modifier (CRM) on low-temperature performance of the binder is not well understood. A CRM swells by absorbing the aromat-ics and light molecular components of asphalt at low interaction temperatures (i.e., 160°C) and dissolves at higher interaction temperatures (i.e., 190°C, 220°C). Each of those activities affects the performance of the CRM asphalt differently. In this research, the activities of CRMs in asphalt controlled accurately through regulating the interaction conditions and the effect of each of those activities on low-servicc-temperature properties of asphalt were studied by using the bending beam rheometer (BBR) and modulated differential scanning calorimetry. The BBR was used to measure the mechanical behavior of CRM asphalt and its liquid phase at low temperatures as a function of CRM dissolution, and modulated differential scanning calorimctry was used to investigate possible changes in glass transition of the liquid phase of the modified binder. Results indicate that the stiffness and m-value of the modified binder are developed in two different manners, and the factors that affect these two parameters are different. Also, results show that through certain interaction conditions, optimization of the low-temperature performance of the CRM asphalt is possible.