The purpose of this study was to investigate the histochemical effect of Jojoongikgi-tang (JIT) on hairless mice induced by DNCB. For the study, DNCB was applied on the infrascapular region of the mices skin and then JIT was orally administered. As a result, the following histochemical changes of the dermis were observed through light and electron microscopes, and statistical data. The results obtained were as follows: 1. In the 2 days experimental group, more histamine mast cells dermis occurred than in the control or normal group when observed under light microscope. When an electron microscope was used, histochemical reactive cells in the dermis were found as mast cells that contained more cytoplasmic granules than in the control or normal group. 2. In the 5 days experimental group, the number of mast cells were decreased over the control or normal group when observed under light microscope. When an electron microscope was used, mast cells in the control contained secretory granules with higher electron density than those of the experimental group. 3. As a result of statistical analysis, the mean value of mast cells in the normal 2 days control and experimental groups was not significantly different (p<0.05). 4. However, the mean values of it in the normal ($19.1000{pm}6.3154$), 5 day control ($103.4500{pm}42.2704$) and 5 day experimental groups ($35.9500{pm}8.5746$) were significantly different (p<0.05). From the above results, it is concluded that JIT is efficient against the purpura induced by DNCB.