Sequential oscillations have been observed in B-Z oscillating system containing vanillin as a single substrate as also along with acetone. Ferroin and MnII ions have been used as catalysts both separately and in combination. Only MnII ions have been found to be suitable for inducing second phase oscillations. Oscillation parameters have been determined potentiometrically. The effects of variations in the concentrations of acid, acetone and vanillin have been investigated. The mechanism of the reaction has been discussed. It is most likely that sequential oscillations are due to vanillin and its oxidation/bromination products.