Ferrites of the type MFe2O4, where M = Zn, Co, and Mg, were prepared via a sol-gel procedure using propylene oxide as a gelating agent. Silver nanoparticles with an average size of 6 nm were prepared in the presence of the ferrite powders in suspension using raffinose as a reducing agent in a basic water solution. Nine samples of the ferrite/silver nanoparticles nanocomposites were prepared in this way with different Ag content. The composites obtained were characterized by XRD, TEM, and UV/Vis spectroscopy. The size distribution of the particles was determined using the data from TEM. By TEM-EDAX, the location of the silver nanoparticles on the ferrite surfaces was determined. Using UV/Vis spectra, the band gap energies for the pure ferrites and the nanocomposites were calculated; the calculated band gap energies were influenced by the presence of the silver nanoparticles. The photocatalytic activity of the silver nanoparticles/ferrite nanocomposites for decomposition of Malachite Green in model water solutions under UV and visible light irradiation was determined. The ZnFe2O4/Ag-NPs nanocomposites were found to be active under visible light irradiation, while the MgFe2O4/silver nanoparticles composites especially active more than the pure MgFe2O4. The presence of silver nanoparticles did not influence the very low photocatalytic activity of CoFe2O4.