The objective on this study was to investigate medicinal protection with KH-19, which was composed of 9 kinds of oriental herbs tonifying the blood, against side effect of chemotherapy in mice and its mechanism through microarray. Not only WBC (white blood cell), and PLT (platelet) as a hematopoiesis toxicity indicator but also spleen weight as an immune toxicity indicator was reduced significantly 7 day after. 5-flurouracil (FU) treatment. However, reduction of WBC, PLT, and spleen weight after 5-FU treatment was significantly recovered by KH-19. For mechanic study on KH-19 action, gene expression in mouse spleen treated 5-FU was compared with gene expression in mouse treated 5-FU and KH-19. The result indicates that 23 genes were increased. in expression level over 2 fold and 41 genes were decreased in expression level more than 2 fold at mouse spleen by KH-19 treatment. KH-19 mechanism may be complicated more than other drug which of mechanism were composed of single compound because KH-19 was composed of various compounds.