In this work, a novel solvent-driven room-temperature synthesis of BiPO4:Eu3+ nanoparticles was presented. By virtue of 11 solvents with different properties and function groups, phase structure and composition of BiPO4:Eu3+ can be systematically tailored. Hexagonal phase (HP) of BiPO4:Eu3+ was obtained in water and hydrophobic organic solvents such as arenes and cyclohexane, while low-temperature monoclinic phase (LTMP) was prepared in hydrophilic alcohols. In other solvents (i.e., hydrophilic ethers, aldehydes, ketones, and carboxylic acids), a mixture of HP and LTMP was formed, in which the relative content of LTMP gradually increased following the above solvent sequence. It is also found that particle sizes of BiPO4:Eu3+ nanoparticles were closely related to the phase structure: HP exhibited a comparatively larger particle size. The phase evolution processes for both polymorphs with varying solvents were investigated in details. Photoluminescence (PL) properties were sensitive to the phase structure and compositions of the final products. With increasing the phase content of LTMP, the lifetimes and quantum yields both increased. The methodology reported here is fundamentally important, which may give a novel insight into the polyrnorph-controlled synthesis for further optimized materials performance.