To study strontium (Sr) incorporation into calcium oxalates (weddellite and whewellite), calcium-strontium oxalate solid solutions (Ca,Sr)[C2O4]nH2O (n = 1, 2) are synthesized and studied by a complex of methods: powder X-ray diraction (PXRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. Two series of solid solutions,isomorphous (Ca,Sr)[C2O4](2.5 - x)H2O) (space group I4/m) and isodimorphous Ca[C2O4]H2O(sp.gr.P21/c)–Sr[C2O4]H2O(sp.gr. P 1), are experimentally detected. The morphogenetic regularities of their crystallization are revealed. The factors controlling this process are discussed.