The main objective in this study is to compare breakage parameters of narrow size fractions of cement clinker taken from the product end and feed end of industrial-scale high pressure grinding rolls (HPGR) in order to assess whether the breakage parameters of clinker broken in HPGR are improved or not. For this purpose, drop weight tests were applied to six narrow size fractions above 3.35 mm, and batch grinding tests were applied to three narrow size fractions below 3.35 mm. It was found that the breakage probabilities of coarse sizes and breakage rates in fine sizes were higher in the HPGR product. This indicated that clinker broken by HPGR contained weaker particles due to cracks and damage imparted. However, no significant weakening was observed for the -19.0+12.7 mm HPGR product. Although HPGR product was found to be weaker than HPGR feed, fragment size distribution of HPGR product did not seem to be finer than that of the HPGR feed at a given loading condition in either the drop weight test or batch grinding test. Also, drop weight tests on HPGR product and HPGR feed showed that the breakage distribution functions of coarse sizes depended on particle size and impact energy (J). Batch grinding tests showed that the specific breakage rates of HPGR product and HPGR feed were non-linear which could be represented with a fast initial breakage rate and a subsequent slow breakage rate. The fast breakage rates of each size fraction of HPGR product were higher than HPGR feed due to cracks induced in clinker by HPGR. However, subsequent slow breakage rates of HPGR product were close to those of HPGR feed due to elimination of cracks and disappearance of weaker particles. Besides, the variation in breakage rates of HPGR product and HPGR feed with ball size and particle size also showed an abnormal breakage zone where ball sizes were insufficient to effectively fracture the coarse particles. Breakage distribution functions of fine sizes of HPGR product and HPGR feed were non-normalizable and depended on particle size to be ground. However, batch grinding of -2.36+1.7 mm and -1.7+1.18 mm HPGR feed yielded the same breakage pattern.