NaYF₄:Yb³⁺/Er³⁺/Pb²⁺ nanocrystals were prepared by a hydrothermal method. The simultaneous phase and size control of NaYF₄:Yb³⁺/Er³⁺ nanocrystals with tunable upconversion luminescence was successfully achieved by tridoping with Pb²⁺ ions. The intensity ratio of ²H_11/2/⁴S_3/2 → ⁴I_15/2 to ⁴F_9/2 → ⁴I_15/2 increased with increasing Pb²⁺ concentration. The upconversion luminescent properties were also investigated.