To establish an efficient system for peroxidase (POD) production by plant cell culture, we investigated the POD activity in 41 cell lines derived from 26 plant species using pyrogallol as substrate. A cell line from sweet potato (Ipomoea batatos cv. White Star) shoot meristem explants cultured on LS medium supplemented with 1 ㎎/ℓ 2,4-D showed the highest activity: 3,500 U/g cell dry wt, about 15 folds higher than that of intact roots of horseradish plants. Furthermore, a cell tine SP-47 having a high growth rate and POD yield was selected by a small cell-aggregate method, of which productivity was about 1.5 times higher than the original cell line in cell suspention culture. A hairy root culture obtained from sweet potato leaf tissue following infection with Agrobacterium rhizogenes strain 15834 also produced a high level of POD: 1,400 U/g dry wt. POD isoenzyme of the cell line and hairy roots of sweet potato showed the same patterns as those of the intacts roots. However, they were prominently different from those of intact roots of horseradish. One major isoenzyme of POD in SP-47 and hairy root covered about 90% of total POD. Due to its high productivity and dominant major isoenzyme, the cell culture system of sweet potato established in this study seems to be suitable for the mass production of POD.