Mixing time and pattern in the impeller-agitated vessel with two-bladed paddle were investigated at various mixing Reynolds numbers by use of two chemical reactions: ordinary decolorizing experiment with iodine and sodium thiosulfate and Beloousov-Zhabotinskii (BZ) periodical reaction experiment. The periodical steady color-variation in BZ reaction system remained after the sufficient time required for the complete decolorization (that is, ordinary mixing time). The sequential spatial color-patterns obtained in steady periodical variation process were similar to the transitional color patterns observed in the decolorization process. The color-patterns obtained in BZ periodical reaction were consistent with the outline of partially mixed regions where the exchange of substance is relatively slow in the vessel and they depended on mixing Reynolds number. The phase of periodical concentration oscillation in each partially mixed region was shifted with one another in spite of the same period of oscillation. Whether the period and/or phase synchronize or not in each partially mixed region would depend on the relative speed between the exchange of substance and the synchronization of periodical oscillation of concentration there. The periodical reaction could become an available tool for the visualization of distribution of those partially mixed regions containing well and bad mixing regions in impeller-agitated vessel. (C) 2012 Elsevier Ltd. All rights reserved.