Crack growth in asphalt concretes or bitumen is a major failure mode at low temperature conditions. However, the vast majority of fracture toughness studies for such materials have been mainly performed on asphalt mixtures and the crack growth analysis and fracture behavior of pure and neat bitumen has rarely been studied in the past. Therefore,Low temperature crack growth behavior of aged and un-aged asphalt binder with penetration grade of 30/40, 60/70 and SBS is investigated experimentally using a new and novel test configuration called inclined notched bend beam (INBB) specimen. A number of fracture toughness experiments were conducted on INBB specimens at two sub-zero temperatures (-15 & -25 oC) and and also on mode I, mode II and different mode I/II mixities. The tests is conducted on two different loading rates (10 & 50 mm/min) to ecaluate influence of each parameter on fracture toughness. It was observed that the fracture toughness of asphalt binder depends significantly on the ageing condition and the load bearing capacity of aged bitumen was up to 60% less than the corresponding fracture resistance of un-aged bitumen. Moreover, the effective fracture toughness was decreased by moving from mode I to mode II and also decreasing the test temperature. The obtained experimental results for both binder types were also evaluated theoretically using a stress based fracture criterion. Especially, at this reseaarch, it is used two important fracture mechanism criterias (GMTS & MTS) to predict frature toughness of binder in different modes. Also. it shows that GMTS can predict the fracture toughness and fracture angle more suitable that MTS. The reduction of mode II and mixed mode I/II fracture toughness values relative to the KIc was also predicted successfully by means of a well-known fracture condition.