Composite materials are widely used in aircraft structures, their relative rigidity/weight confers their advantage over metal structures, and the stacking sequence plays an important role for their use. The objective of this work is to analyze by the finite element method the mechanical behavior of a single lap joint of composite/composite type under a tensile load. In order to see the effects on the failure load, two basic parameters are taken into consideration; the stacking sequence of composite and thickness of each layer constituting the composite. Calculation of the failure load is made numerically with the ABAQUS code using the developed technique of VCCT (Virtual Crack Closure Technique) based on fracture mechanics. Finally, the influence of the bonding defect on the failure load is analyzed. The results clearly show the importance of optimizing fiber orientation and hence the stacking sequence for proper use of composite in bonded assemblies.