Heterophasic ethylene-propylene copolymers represent the most commercially relevant group of impact modified polypropylene. These polypropylene resins serve typically in engineering and automotive applications where high impact strength is required within relative broad temperature range. The heterophasic ethylene-propylene copolymers comprise a polypropylene (PP) matrix and an ethylene propylene copolymer (EPC) dispersed phase. In contrast to the mechanical PP/EPC blends, they are synthesized in a sequential copolymerization process in a reactor or reactor cascade. Utilization of such an in situ blending technique enables materials design to be performed readily on molecular level, thus giving a far wider possibility for structure and accordingly property tailoring.This work encompasses comprehensive structural and mechanical characterization of heterophasic ethylene-propylene copolymers as affected by variation of different system parameters. All the employed materials were produced in a batch reactor under industrially relevant conditions. The main focus was on exploiting the opportunities given by a proper process control in the polymerization stage for producing reactor blends of targeted molecular structure and interrelating it to their macroscopic mechanical performance. The main variables utilized were EPC composition (ethylene/propylene ratio) as well as molecular weight of EPC and PP phases.