A novel approach to the synthesis of Gd-Si oxide mesoporous nanoparticles with a high Gd(3+) atom density and pre-formed morphology is presented. Prussian blue analogue Gd(H2O)4[Fe(CN)6], a metal organic framework that crystallizes in the orthorhombic system, is used for the first time as a sacrificial template by a reaction with soluble silicate. Simultaneous and stoichiometric condensation of gadolinium hydroxide and silica takes place, leading to dense and monodispersed nanoparticles that preserve the original shape and size of the Prussian blue analogue crystals. Then, porosity is developed by incorporation of cetyltrimethylammonium bromide under hydrothermal conditions. The obtained Gd-Si mesoporous oxide particles present a dual morphology of nanocrosses and nanorods and large surface areas.