The new amorphous alloy with the composition of (Tm67Cu33)80Al20 is designed with the deep binary eutectic composition of Tm67Cu33. The (Tm67Cu33)80Al20 alloy exhibits a fully amorphous structure. As the Cu and Al elements have no magnetic moment, there is only Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetic interaction existing in (Tm67Cu33)80Al20 amorphous alloy, leading to its low Curie temperature (TC) (4.4 ± 0.3 K). The peak value of the magnetic entropy change and refrigeration capacity of the (Tm67Cu33)80Al20 amorphous alloy under a magnetic field change of 5 T are 13.4 ± 0.7 J kg−1K − 1 and 174.2 ± 10.5 J kg−1, respectively. The (Tm67Cu33)80Al20 amorphous alloy possesses a relatively high magnetocaloric response compared with that of the reported RE-based alloys with the similar TC. These results indicate that the (Tm67Cu33)80Al20 amorphous alloy could be a promising candidate material for magnetic refrigeration applications in the liquid helium temperature range.