The particularities of complex substituted calcium phosphates formation in the aqueous solution of system Ca2+-M+-Cs+-PO43--CO32--NO3- (M+ - Na, K) were investigated by wet precipitation method at fixed molar ratios CaP/P = 1.67 and CO32-/PO43- = 1 and different values M+/Cs+ = 1.0 or 2.0 at the temperature 25 °C. Possibility of cesium ions incorporation into apatite-related structure of complex substituted calcium phosphate was firstly investigated under conditions of wet precipitation in the presenceof carbonate and alkaline metal ions. The obtained powders were characterized by powder X-ray diffraction, FTIR spectroscopy, scanning electron microscopy, TG/DTA and elemental analysis. Based on the combination of elemental analyses (X-ray fluorescence, EDX, CHN methods) and TG/DTA data for prepared samples, it was found, that the changing of molar ratio M+/Cs+ from 1.0 to 2.0 caused increasing of M+-content (close to 16 % and 12 % for Na+ and K+, respectively) and amount of carbonate for Na+-containing sample (close 36 %) while the amount of carbonate in K+-containing samples decreases on 30 %. The obtained results indicate that alkaline metals nature affects the substitution degree of phosphate by carbonate-group.