A novel two-step constrained aging (CA) treatment, in the form of CA firstly at 500 °C for 1 h and then CA at 300 °C for 39 h, is proposed to obtain enhanced two-way shape memory effect (TWSME) and elevated R-phase transformation temperatures of the Ni51Ti49 alloy strip fabricated by rapid solidification technique. The two-step constrained aged Ni51Ti49 alloy strip possesses a much increased recovery ratio of 96.4% in the fully martensitic state, and elevated R-phase transformation start and finish temperatures of 60.2 °C and 40.9 °C respectively, compared with these of the alloy subjected to the one-step CA treatment. Higher recovery ratio and elevated R-phase transformation temperatures are attributed to preferentially oriented lenticular coherent Ni4Ti3 precipitates, with an average length of 149.1 ± 14.3 nm, dispersed homogeneously in the NiTi matrix. The first-step CA with a relatively high aging temperature triggers the fast growth of Ni4Ti3 precipitates, while the second-step CA with a low aging temperature leads to decrease of the solid solubility of Ni atoms and promotes further precipitation of Ni atoms and thus induces formation and growth of Ni4Ti3 precipitates.