Thin films of 1‐2‐3 high Tcsuperconductors were fabricated by RF magnetron sputtering from a several compound oxide target. Film composition was studied as a function of oxygen content of the target, power density, temperature, and pressure. Compositional analysis was performed by Rutherford backscattering spectroscopy and energy dispersive x‐ray analysis before and after annealing treatment. The resulting film compositions were then related to the aforementioned sputtering parameters so that optimal sputtering conditions for achieving consistent 1‐2‐3 film stoichiometry could be established.