Optimum alio-valent doping with yttrium sulphate creating 7% vacancy concentration provided promising features from sensor application view. This provides a better option over green Silver Sulphate. The sensors fabricated with the modified sulphate based silver ion conducting solid electrolyte, silver-silver sulphate reference electrode and test gas (Pt) electrodes has been tested over the range of 50-1000 ppm SO2 blended in constant oxygen-partial pressure and argon at 400 o C. A promising sensor characteristic behaviour is exhibited by the modified electrolyte - solid solution of silver sulphate with yttrium.