Substitution of Ca for Y does not increase the maximum oxidation state of the (CuO 3-δ) (3- x)- layers of Y 1- xCa xBa 2Cu 3O 7- δ (0 ≤ x < 0.3); as x increases so does the minimum value of δ obtained by annealing in an oxygen atmosphere at temperatures 350-450°C. The superconducting transition temperature Tc decreases from 87 K for x = 0 to about 66 K for x = 0.3 despite a nearly constant total formal oxidation state for the copper. A broad transition for the x = 0.2 and 0.3 samples suggests a tendency to segregate into two phases of different oxygen content having different values of Tc. The normal state remains metallic above Tc. The lattice parameter variation with x has been monitored for samples air-quenched from 450°C.