The two-dimensional (2D) delamination behavior of composite laminates under quasi-static out-of-plane opening loads has been experimentally investigated. A novel design and experimental set-up for fiber-reinforced polymer (FRP) laminated plates with a circular embedded pre-crack was developed. Increasing load-displacement curves were obtained due to the increasing crack front length during propagation. Throughout the loading process, stiffening and softening mechanisms were activated. The stretching of delaminated part of the laminates constituted the main stiffening mechanism. Once the crack started growing, a corresponding softening due to crack propagation occurred together with a secondary stiffening mechanism, fiber-bridging. These stiffness-related mechanisms were reflected in the compliance.