The size of the PbSnF4 particles incorporated into the sensing electrode (SE) influences the response properties, particularly, the mean 90% response time t(90)(m), of the amperometric oxygen sensor Ag\Ag6I4WO4\PbSnF4 (PSF)\SE (a mixture of SnO2-coated 9Al(2)O(3).2B(2)O(3), whiskers, iron phthalocyanine, and PSF). With incorporation of the sheetlike PSF particles of similar to 18 mu m as well as the conductive whiskers, the sensor responded unprecedentedly fast [t(90)(m)approximate to 25 s] at room temperature, compared with t(90)(m) for known solid-state electrochemical oxygen sensors. The results suggest that the SE mixture should be designed tip realize fast response considering the dispersed state, which depends on the morphological feature of all the SE components.