BaMoO(4) with 3D hierarchical multilayer disk-like and nest-like architectures self-assembled from 2D nanosheets was successfully synthesized via a microwave-assisted hydrothermal route without any surfactant. The as-prepared products were characterized by X-ray powder diffractometer (XRD), scanning electron microscope (SEM), field emission transmission electron microscope (FE-TEM), and photoluminescence (PL) spectrometer. The results show that the reaction parameters, including pH value, reactant concentration, and molar ratio of [Ba(2+)]/[MoO(4)(2-)], played important roles on the morphologies of the final products. And the formation mechanism of 3D hierarchical architectures is a stepwise oriented aggregation-based self-assembly process. The superstructure characteristic of 3D nest-like BaMoO(4) architecture was observed in HRTEM image and the corresponding fast Fourier transform (FFT) for the first time, and the superlattice reflections with non-integer indices occurred around the subcell reflections at ±1/6(2a*+2c*). Room temperature photoluminescence spectra of 3D BaMoO(4) architectures reveal a strong and broad blue emission, and the 3D nest-like architectures own the enhanced intensity than multilayer disks.