The irreversible properties of a rare-earth high-T c superconductor are investigated using grain-aligned Sm 1-x Eu x Ba 2 Cu 3 O 7−δ (x = 0.0, 0.3, 0.5, 0.7, and 0.9) samples. The samples were synthesized using the usual solid–state reaction method. It is found that the transition temperature T c and the critical current density J c calculated by the Bean model are significantly improved in the optimally doped samples (x = 0.5 and 0.7). Furthermore, the double logarithmic graph of the irreversibility line B irr in the grain-aligned series samples obeys approximately a power law dependence (1−T/Tc)n. Results show that in the case of optimally doped samples with x = 0.5 and 0.7 the graph of B irr is fitted well with the relation (1−T/Tc)n with the model-dependent parameter n ∼1.5 without any crossover in the entire temperature range, while in samples with x = 0.0, 0.3, and 0.9 B irr does show a prominent crossover and can be characterized with n ∼1.5 only near T c , above which B irr varies more rapidly. Finally, it is suggested that B irr is strongly dependent on the extrinsic properties of our grain-aligned samples.