There is an urgent critical need for the development of clinically relevant tissue-engineered large bone substitutes that can promote early vascularization after transplantation. To promote rapid blood vessel growth in the engineered tissue, we preincubated aortic fragments, as well as, co-cultures of aortic fragments and osteoblast-like cells in matrigel-filled PLGA scaffolds before implantation into the dorsal skinfold chambers of balb/c mice. Despite an acceptable and low inflammatory response, preincubated aortic fragments accelerate early angiogenesis of tissue-engineered constructs; the angiogenesis was found to occur faster than that observed in previous studies. Thus, the time-period for achieving a denser microvascular network could be reduced to half. In addition, co-culture with osteoblasts enhances this angiogenic effect significantly (against preincubated aortic fragments alone). During the preincubation period, aortic fragments begin to form a network of vessel-like structures additionally supported by osteoblast-like cells. After transplantation, further development of a dense microvasculature continues rapidly. Therefore, preincubation of aortic fragments, especially in co-culture with osteoblast-like cells, in 3D extracellular matrices supports the rapid vascularization of tissue-engineered constructs. This method is a promising approach to establish a dense microvascular network in these constructs.