This paper investigates the blast fragmentation of a mortar cylinder by numerical simulations. The aim of the project is to understand the underlying mechanisms causing blast induced fines. Two numerical methods: Finite and Discrete Element Methods (FEM, DEM) with explicit time integration were used and the results were compared with the results of blasting tests. In FEM thin cylindrical disk (Ø140 mm) with 1 layer of 3D continuum elements and in DEM a 3D cylinder with Ø140×200 mm were modelled. They were loaded by a pressure evolution acting on borehole wall. Both models reproduce realistic crack patterns consisting of through-going radial cracks, with branching and interconnecting cracks, around a crushed zone at the borehole. The FEM models, however, for slight changes contain unrealistic areas of deleted elements, whereas the DEM models were more robust and delivered realistic fragment size distribution of the expected Swebrec function type.