Size controlled cyano-bridged coordination polymer nanoparticles Mn+/[M'(CN)(m)](3-) (where Mn+=Ni2+, Fe2+, Co2+ and M'=Fe3+, Co3+(m=6); Mo5+ (m=8)) have been synthesised and organised by using mesostructured hybrid silica hosts of various sizes (3.4, 5.3 and 7.5 nm) containing -(CH2)(2)C5H4N groups. The obtained composite materials were studied by transmission electronic microscopy (TEM), infrared and electronic spectroscopies, nitrogen sorption, X-ray diffraction and magnetic measurements. These analyses reveal the formation of hetero- or homo-metallic cyano-bridged nanoparticles with controlled stoichiometry uniform in size and shape within the silica matrix. The size of the nanoparticles is controlled by the pore size of the silica used. The magnetic study of these nanocomposite materials reveal an appearance of a spin-glass like regime which can be caused by a spin frustration on the surface of the nanoparticles and/or by interparticle magnetostatic interactions.