Geometrical effects on the oscillatory behavior during the reduction of iodate in an alkaline solution have been studied in detail. We have found that the geometrical factors greatly affect the oscillatory behavior when the iodate concentration is smaller, and chaos appears on the electrodes with smaller size or smoother surface, whereas at higher iodate concentration, the influence from the geometrical factors is minor and periodic behavior occurs instead, though some differences still exist in the waveforms with different roughness. The geometrical factors affect mainly the convection mass transfer of the iodate induced by the hydrogen evolution, in addition to the different adsorption.