Sheet-like Bi2MoO6:Ln3+ nanocrystals were synthesized by a hydrothermal method. The crystalline size of Bi2MoO6:Ln3+ (Ln = Eu and Gd) nanocrystals changes gradually with the increasing of Ln3+ content in the reaction solutions. The photoluminescence properties of Bi2MoO6:Ln3+ nanocrystals were investigated in detail. In the emission spectra of Bi2MoO6:Eu3+ nanocrystals the 5D0 →7F2 is much stronger than the 5D0 →7F1 and is the strongest when the excitation is performed at 467 nm. The relative intensity of the transitions from Eu3+ increased with increasing Eu3+ concentrations, up to about 50 mol%, and then decreased abruptly. In the excitation spectra of Bi2MoO6:Eu3+ (30%)/Gd3+ monitored at 618 nm, the 7F0 → 5D2 (∼467 nm) transition is dominating when the Gd3+ concentrations were 10% or 20%. When the Gd3+ concentration was 30%, the 7F0 → 5D1 (∼538 nm) transition is dominating. In addition, the photocatalytic activity of Bi2MoO6:Eu3+ was evaluated by the degradation of rhodamine B (RhB) aqueous solution under simulated solar light. The best photocatalytic performance was observed when the Eu3+ concentration was 1%.