Flowerlike hierarchical Bi2MoO6 and Bi2MoO6:Er3+ microspheres were synthesized by a hydrothermal method. The crystalline size of microspheres decreases with increasing Er3+ concentration. The incorporation of Er3+ has no evident influence on the morphology of Bi2MoO6. The photocatalytic activity of microspheres was evaluated by the degradation of rhodamine B (RhB) aqueous solution under simulated solar light. The best photocatalytic performance was observed when the Er3+ concentration was 0.5%. In addition to the aforementioned high photocatalytic activity, the Bi2MoO6:Er3+ microspheres can emit pure green upconversion (UC) luminescence (2H11/2/4S3/2 → 4I15/2) under 980 nm excitation. We suggest that the enhancement of photocatalytic activity of Bi2MoO6:Er3+(0.5%) is related to the UC luminescence of Er3+ ions. In addition, the BET surface areas of samples increased with increasing Er3+ concentration, which is also benefit for RhB adsorption.