Abstract: A series of Y_1-xCa_xBa₂Cu₃O_7-y superconductor have been investigated. For x≤0.15,the Y³⁺ is replaced by Ca²⁺ in 123 phase and the solid solutions are formed. That leads to the slight increase of the lattice parameters of orthorhombic phase. When the contents of Ca increase, the contents of Cu³⁺ increase but their T_c decrease. It is considered that the properties of neighboring Cu(2)-O plane are affected, when the Y³⁺ is substituted by Ca²⁺ then it results in the T_c dropping. It is shown that the properties of Cu(2)-O plane are very important to superconductivity.

Key words: Y-Ba-Cu-O superconductor, superconductivity, Ca²⁺ dropping