Gamma-Ray Bursts (GRBs) are brief high-energy signals revealing the explosion of massive stars at large distances (z ~ 1). The burst of high energy photons is usually followed by an afterglow visible at optical wavelength during a few hours to a few days. We summarize here the scientific motivations for searching GRB afterglows in the CFHTLS, independently of the detection of the GRB itself by spaceborn detectors.