Safe performance of connecting joint applied to different concrete ages is highly important when joints is placed in composite structures since joint is involved in mutual deformation of precast and monolithic concretes. This experimental study was carried out to determine how type of joint influence on it bearing capacity when perceiving shearing forces. The tests were carried out on a specially manufactured horizontal bench and a vertical press, which provided a shear force in the samples of different ages and with different concrete strength (light monolithic and heavy precast concretes). The following options of the joint were considered: a smooth surface, where the connection is done only by the forces of adhesion and friction; a joint with keys, the spacing of which varied; and a joint with the use of cross reinforcement. This paper determines nuances of the load-bearing capacity exhaustion in a composite structure at shear depending on the type of joint of lightweight monolithic and heavy precast concrete. A comparative analysis of the results obtained in the experimental studies and the data of previous studies has been carried out. The highest bearing capacity under shearing loads was determined in the joint with the cross reinforcement. Moreover, it was noted that keyed connection of concretes let guarantee sufficiently safe performance of connection.