Recently, high attention has been paid to template synthesis as a method for obtaining nanostructures with predetermined shapes and sizes. This is an obvious approach, in which the size and shape of the pores limit the geometry of the nanostructures formed inside them. As a result, nanostructures completely repeat the shape of the template pores. However, in some cases, the morphology of the resulting structures may differ from the shape of the template, and often these differences are not explained. This is a gap in fundamental knowledge on the mechanism of nanostructure growth in a limited template pore volume. In this work, we partially solve this problem. Using silver as an example, it is shown that by changing only the pore volume, without changing other chemical kinetic conditions, it is possible to controllably create nanostructures with complex geometry. Possible morphologies of nanostructures, such as crystallites, dendrites and “sunflower-like" structures, formed at critical pore diameters, have been identified. The main points inherent to the formation of silver nanostructures in the pores of the SiO2/Si template using the electroless galvanic displacement method were highlighted. The growth mechanism of silver nanostructures in a limited pore volume has been studied and discussed in details.