The purpose of this project is to observe how the joints affect rock fragmentation. In order to see the influence of the joints, the properties of the mortar blocks used in the testing were kept similar as well as delay times, explosives, detonators but not the joint families in the blocks. In order to succeed, different types of jointed lab-scale blocks were prepared by Jonas Hyldahl. These blocks were measured, weighed and volumes were calculated. The hole lengths and widths, and the P-S wave speeds of the blocks were measured. The blocks were blasted as 3 single rows under the similar circumstances. Right after blasting the rows, photographs were taken in order to make roughness calculations in Blast Matrix by Orhan Altürk. After the each row was blasted, the fragments and dust were carefully collected into the buckets for sieving tests in the laboratory. The remaining parts of the blocks which were left after blasting were then extracted carefully and sliced into 4 equal parts. These slices were subjected to dye penetrants to make the cracks on the slice faces visible. Afterwards, the slice faces were photographed (the most suitable upper or lower faces were always chosen). These photographs were used for crack detection and AutoCAD 3D modelling. In the modelling sequence, the crack families were identified and cracks were counted with the help of AutoCAD. The data of the crack families were used for comparison and analysis with statistical methods. Outputs of the analysis were interpreted in terms of if joints possibly influence the fragmentation. In addition, the sieving data was also analyzed, the K30, K50 and K80 fragment sizes of the different jointed blocks were compared and graphed. Results show that, different crack families occur in the jointed blocks and in some cases these cracks lead to large breakage behind the line of drill holes in the blocks. On the JS1, JS2 and JS4 blocks, these cracks occur at the end of the joints and form a bow shape between joints. On the other hand, in JS3 blocks these joint related cracks were following a path from the borehole to the end of the joint. Furthermore, the obtained K30, K50 and K80 results show that the fragmentation of the jointed blocks is finer than the fragmentation of the reference blocks.