Nanoparticles of a-Bi 2 Mo 3 O 12 were prepared by the Pechini method. The process of formation of the bismuth molybdate was followed by simultaneous thermogravimetric and differential thermal analysis (TGA/DTA). Different samples of a-Bi 2 Mo 3 O 12 were obtained at 400, 450, and 500°C, and characterized by X-ray powder diffraction (XRD), nitrogen physisorption (BET), and scanning electron microscopy (SEM). When observed by SEM, the morphology of the sample obtained at the lowest temperature consisted of semi-spherical particles with an average diameter of 150 nm. On the other hand, the highest calcination temperature led to the formation of sintered particles of 500-600 nm. The photocatalytic activity of a-Bi 2 Mo 3 O 12 was tested by photodegradation of the organic dyes rhodamine B (rhB) and indigo carmine (IC) under visible-light irradiation. The bismuth molybdate nanoparticles were able to bleach aqueous solutions of both organic dyes. The sample obtained at 400°C was the best photocatalyst with half-lives, t 1/2 , of 108 and 154 min for rhB and IC, respectively.