Double cantilever beam (DCB) specimens fabricated from 15 plies of a plain woven prepreg (G0814/913) arranged in a multi-directional (MD) layup were tested by means of constant amplitude fatigue cycles under displacement control. The prepreg consists of carbon fibers in an epoxy matrix. Eight specimens were tested. Four different displacement cyclic ratios were used, namely 0.1, 0.33, 0.5 and 0.75. The delamination propagation rate da/dN was calculated from the experimental data and plotted using a modified Paris law with different functions of the mode I energy release rate GI. One of these functions led to a collapse of all of the data into one master curve.