Urchin-like LaPO₄ hollow spheres were successfully synthesized by a facile solution route using citric acid (CA) as a structure-directing agent. The size of the three-dimensional (3D) hollow spheres was tuned by changing the concentration of CA. The formation mechanism of the 3D LaPO₄ hollow spheres was revealed by studying the time-dependent morphology evolution process. Importantly, compared with monodispersed one-dimensional (1D) LaPO₄ nanorods, the 3D LaPO₄ hollow spheres self-assembled from nanorods showed a 6.8-fold enhancement in photocatalytic activity for CO₂ reduction, which is attributed to the synergistic effect of their hierarchical hollow structure, higher light-harvesting capacity, and faster electron transfer. Our findings provide not only a simple, facile method for the synthesis of hierarchical hollow micro/nanoarchitectures but also an efficient route for enhancing the photocatalytic performance.