New oxide superconductors in the Sr-Bi-Cu-O system were prepared by the conventional processing techniques consisting of mixing, pressing and sintering. The compositions of the superconductors are located in a range surrounded by CuO, SrCu2O3 and Sr0.9Bi1.1O2.55. No distinct compositional change in the critical temperature,T c, is observed and the value is 8 to 9 K at onset and 4 to 5 K at zero resistance. The zero resistance value increases on replacement of strontium by sodium or potassium which have different atomic valences and a nearly equal ionic radii compared to strontium, accompanied by an increase in the positive slope of electrical resistance and reaches a maximum value of 6.7 K for Sr0.9Na0.1 Bi1Cu2O4.45 and 5.9 K for Sr0.9K0.1Bi1Cu2O4.45. The further increase in sodium and potassium content brings about the disappearance of superconductivity, along with an extreme increase in the negative slope of electrical resistance. The increase inT c for the Sr-Bi-Cu oxides with the replacement by sodium or potassium is probably because the replacement gives rise to a change in the valence of copper atoms and/or the formation of an oxygen-deficient structure.