Most studies on the pinning properties and the relating vortex nature of the RE123 system have been performed at high temperatures around 77 K. However, the pinning characteristics of RE123 at low temperatures have not been well understood yet, while extensive applications using the crycooling system are also strongly expected. In the present study, the J_c-H-T properties have been studied Gd123 single crystal with low level Gd substitution for Ba and Y123 single crystals substituted by small amount of impurity ions, such as Sr and Co, which improve J_c properties accompanying huge peal effect in their J_c-H curves. It was found the increases in F_p as the temperature of the impurity doped Y123 samples decreased were much larger than that of the Gd123 sample, while the Gd123 sample exhibited higher J_c than of the Y123 samples above 77 K. The J_c performance of the Gd123 sample below 50 K was even lower than that of the undoped Y123 sample. This strongly indicates that the RE123 with RE/Ba substitution is not appropriate for low-temperature applications, such as high-field magnets, despite their good J_c performance at high temperatures e.g. 77 K.