The effect of additional metal doping of high-T_c (critical temperature) super-conductors (HTSC) on the superconductive properties and crystal growth has been investigated using the bulk samples made by conventional sintering and the melt-quench process, and thin films by RF-sputtering. It was found that the formation of the high-T_c phase is remarkably promoted and superconductive properties are improved by the metal addition of an adequate amount of the Ba or Sb element to Bi-compound HTSC and Ag element to Y-compound HTSC.