This paper reports on fracture properties of the interface in high strength concrete. The fracture properties included in this study are: strength, fracture toughness and ductility factors. Experiments were conducted on composite specimens in Mode-I and Mode-II loading effects. Two types of composite specimens were designed. In the first type, the mortar was cast against the hardened concrete on only one face, and in the second type, the mortar was cast on both the faces of the aggregate material. The latter type has been designated as sandwiched type. For Mode-I case, both the types of composite specimens were used, while for the Mode-II loading only sandwiched type of composite specimens were adopted. Two types of aggregate materials have been adopted: granite rock and hardened HSC. In the case of granite rock aggregates, rough and smooth surfaces were used, while in the case of HSC concrete, rough, smooth and casting surfaces have been adopted. Three types of mortar mixes were used at 0.40 water-binder ratio with 1:3, 1:2 and 1:4 cement-sand ratios. Silica fume was used 10% by weight of cement. Strong interface has been noticed with rough aggregate surface. The fracture toughness of the interface seems to be very high with rougher aggregate surface in Mode-I. The type of mortar matrix significantly alters the type of interface. The influence of size of interface area on the fracture properties has also been reported. Size effect seems to be clearly observed in Mode-II loading. The fracture toughness increases as the roughness and the inclination of the aggregate surface increases. Interestingly, the sandwiched composite specimens exhibited decreasing fracture toughness with increase in the interface area. Ductility factor, defined as the fracture energy per unit of peak load decreases as the surface area of the interface increases in Series II and III specimens. The CMODc seems to be slightly higher with rough aggregate surface. The interface exhibits significantly brittle behavior showing catastrophic failure, which indicates a possible application of LEFM to the interface.