The Dugdale model [i] is widely used to give an estimate of the plastic zone size for finite or semi-infinite geometries. Inasmuch as the Dugdale model is an approximate model and is computationally solved as an elasticity problem with the band of yield stress around the crack tip considered as an additional load system, the following simple method for estimating plastic zone lengths for edge cracks seems plausible. The method is similar to Folias's approach [2] in estimating plastic zone sizes for a centre crack in a thin plate.