Instabilities of the Belousov-Zhabotinsky reaction were investigated in a Taylor vortex flow reactor with constant axial flow regarded as a one-dimensional open reaction-diffusion system. The effective axial diffusion coefficient was used as one of the controlling parameters, and changed by varying the rotating speed of the inner cylinder. Effluent from an isothermal continuous stirred tank reactor was supplied as the feed into the test reactor so as to clearly specify the inlet condition of concentration oscillation. The feed rate was changed as another controlling parameter. Irregular disturbances appeared at low-concentrations of Ce4+ when the inlet condition was singly periodic oscillation, whereas no remarkable irregular oscillation could be found when the inlet condition was dynamical equilibrium. The spatio-temporal oscillation patterns were successfully described qualitatively by a numerical simulation based on the ’Coupled Map Lattice’ method using an Oregonator reaction model. The numerical results also suggested that complex spatial and temporal behavior occurred under the inlet condition of singly periodic oscillation.