AbstractThe solubility in the Cu(HCOO)2–Sr(HCOO)2–H2O system has been studied by the method of physico‐chemical analysis at 25 and 50 °C. It has been established that two double salts are formed in the system: CuSr2(HCOO)6· H2O at 25 °C and CuSr(HCOO)4· 4 H2O at 50 °C. The latter salt has not yet been described in the literature. It has been characterized by X‐ray powder diffraction and DT and TG analysis. CuSr(HCOO)4· 4 H2O crystallizes in the triclinic system with lattice parametersa= 12.376(6) Å,b= 13.394(4) Å,c= 11.508(6) Å, α = 93.38(3)°, β = 94.01(3)°, γ = 75.04(3)°. Dehydration