We have designed sensors based on Ag nanoparticles synthesized in situ on the vaterite beads. In this article we demonstrate an approach to produce size controllable spherical and elliptical vaterite particles and discuss time-dependent in situ Ag nanoparticles synthesis and its potential effect on surface-enhanced Raman scattering. The time dependent silver reduction synthesis in inorganic porous particles allows to regulate the number and size of Ag nanoparticles. It is shown that the irregular surface and high porosity of vaterite particles and large amount (surface filling factor) of the Ag nanoparticles are the critical parameters to increase the SERS signal to 104 times. Such inorganic composites have a huge potential in medical applications; soon they provide an opportunity to study intracellular processes in vivo. The detailed characterization of the microstructure of these composites was studied by scanning and transmission electron microscopy, including 3D visualization and energy dispersive x-ray microanalysis.