The aim of the study was to determine the effect of the genotype and ageing time on pH, water holding capacity, shear force and energy, and the myofibrillar index of m. longissimus lumborum and m. semitendinosus muscles in semi-intensively fed bulls. Carcass value indices and the chemical composition of the muscles depending on the genetic group were assessed as well. The study involved 46 young bulls from four genetic groups, i.e. the Hereford breed (HER - 8 bulls), the Limousin breed (LIM - 8 bulls), commercial cross-breeds (MT - 14 bulls), and the Polish Black-and-White Holstein-Friesian breed (PHF - 16 bulls). The analyses showed that the semi-intensive fattening system ensures production of carcasses with satisfactory slaughter yield and quality parameters (good musculature and moderate fatness). The best quality parameters were determined in the meat from the LIM and MT young bulls, whereas the poorest results were exhibited by the PHF beef. The ageing time had a positive effect on the meat quality parameters (especially tenderness and color), contributing to a significant reduction in the differences between the genotypes observed in the initial postmortem period. The results of the shear force and myofibrillar index, i.e. parameters of meat tenderness, suggest that a 14-day ageing period seems to be the necessary minimum. This period should even be extended in the case of the LL muscle of HER and PHF young bulls or the ST muscle of HER, MT, and PHF young bulls. Further research with consumer assessment is therefore advisable to determine the optimal ageing time of beef produced in the country.