In this study, the load-carrying capacities of the mechanical butt joints have been obtained experimentally and numerically under three point bending load. Composite plates have been jointed as a mechanical butt joint with the jointing element. The shape of I profile has been used as the geometric jointing element throughout the study. It has been determined that the results obtained from the Abaqus finite elements program and the data obtained from the experiment support each other. According to the investigation optimum jointing parameters have been found with the h/2w ratio of 0.5, b/w ratio of 0.5 and z/b ratio of 0.5. It has been concluded that considering that the first damage will occur on the jointing element with profile I before the jointed composite specimens and consequently composite structures are totally damaged, jointed composite structures can be made to work longer through the repairment of the jointing element.