Abstract: The Lewis lung carcinoma (LLC) metastatic mouse model was used to investigate the effects of gefitinib and Sijunzi Tang (SJZ) on pre-metastatic niche. The experimental protocol was approved by the Ethics Committee which belongs to Cancer Hospital, Chinese Academy of Medical Sciences. To generate spontaneous lung metastatic models, 1×10⁶ luciferase-labeled LLC cells were injected subcutaneously in the shaved right flank of mice. One day after LLC inoculation, the mice were randomly divided into model (saline), gefitinib (50 mg·kg^-1) treatment, SJZ treatment (25.74 g·kg^-1), and co-treatment gefitinib with SJZ groups, with intragastrical administration. After 14 days of continuous administration, tumor size was detected by IVIS^® Spectrum system. The number of monocytes and neutrophils and the expression levels of chemokine receptors (CXCR1, CCR2) and carcinogenic gene (c-Kit), in peripheral blood, spleen and lung tissues of mice were determined by flow cytometry. The contents of interleukin-IL-1α (IL-1α) and interleukin-6 (IL-6) were detected by the enzyme linked immunosorbent assay (ELISA). After 21 days of treatment, tumors were surgically removed, weighed and the tumor volume was measured with vernier caliper and the antitumor effect of co-administration was evaluated. After 45 days of administration, the survival of mice was recorded. The results of flow cytometry showed that the percentage of neutrophils in gefitinib group, SJZ group, and co-treatment group was significantly decreased in the lung tissue compared to the model group (P<0.05 or P<0.01), but there was no significant difference between three treatment groups (P>0.05). In the mouse peripheral blood and lung tissue, compared with the model group, the expression levels of CXCR1, CCR2 and c-Kit on the surface of neutrophils and monocytes in SJZ group and co-treatment group decreased or decreased significantly (P<0.01 or P<0.05). However, there was a significant increase in the expression level of c-Kit on the surface of monocytes (P<0.05). In the mouse spleen tissue, the expression levels of CXCR1, CCR2 and c-Kit in the gefitinib group increased significantly (P<0.05), while decreased significantly in SJZ or co-treatment group (P<0.05). The results of ELISA showed that the content of IL-1α in SJZ group decreased significantly in the plasma of the mice compared with the model group (P<0.01) and the content of IL-6 in co-treatment group decreased significantly (P<0.05). Compared with the gefitinib group, the content of IL-1 in the co-treatment group decreased significantly (P<0.05). In the tumor tissues of mice, compared with the model group, the content of IL-1α in the co-treatment group decreased significantly (P<0.05). Furthermore, the content of IL-1α in co-administrated group and IL-6 in SJZ or co-treatment group decreased significantly compared with the gefitinib group (P<0.05). After 21 days of continuous administration, the tumor inhibition rates of gefitinib group, SJZ group and co-administrated group were 45.7%, 38.4%, and 84.8%, respectively. After 45 days of administration, the survival rate of the model group was 0%, whereas the gefitinib, SJZ or co-treatment group has a survival rate of 40%, 60%, or 60%, respectively. In summary, our study illustrated that Sijunzi Tang could improve the anti-tumor effect of gefitinib by regulating pre-metastatic niche.