The effect of reactor volume on concentration oscillations in the cerium-catalyzed Belousov-Zhabotinsky reaction is observed by varying mean residence time of feed as a bifurcation parameter. Three CSTRs different in volume were used in the experiment with the same stirring conditions. Chemical oscillations are investigated by measuring the redox potential between Ce3+ and Ce4+ using a Pt-wire electrode. Owing to the effect of nonlinear coupling between essential chemical oscillations and external forcing oscillations by the peristaltic pump, chaotic oscillations occur in shorter mean residence time. It has been found that this coupling effect affects the greater concentration oscillations in smaller CSTR. At the bifurcation point between single-peak oscillation and chaotic oscillation state, intermittent oscillations are observed. It has been found that stable single-peak oscillations can be observed throughout wide mean-residence-time region with increasing volume of reactor.