Abstract: Objective: To investigate the effects of the micro-molecular compound 4-methyl- 3-nitro-benzoic acid on drug toxicity, migration capacity of various malignant tumor cells and inhibition of tumor growth on mice.Methods:The dos -age of 4-methyl- 3-nitro-benzoic acid was arranged by geometric series, and then the half lethal dose was measured on mice in vivo. Chemotaxis assay was performed to detect the effects of 4-methyl- 3-nitro-benzoic acid on cell migration ca pacity of the lung cancer cells A549 , liver cancer cells SSMC- 7721, malignant melanoma cells LiBr and gastric cancer cells MGC-803 in vitro. In vivo, BL 6-B16 cells were injected to C 57 mice with normal sodium as the control. The effects of 4-methyl- 3-nitro-benzoic acid on the growth of the mouse-transplanted tumors were observed after intra-gastric administra -tion. The body weight of the mice was recorded as another measure to estimate the toxic effect of the drug, 4-methyl- 3-ni-tro-benzoic acid. Results: It was shown by acute toxicity testing that the half lethal dose (LD 50) of 4-methyl- 3-nitro-benzoic acid in mice in vivo is 771 .73mg/kg. Chemotaxis assay showed that4-methyl- 3-nitro-benzoic acid could overtly and mark -edly inhibit the cell migration of many tumor cells with2.0 μ M as the optimal inhibi ting concentration. 4-methyl- 3-nitro-ben-zoic acid could inhibit the growth of mouse-transplanted melanoma, and the tumor volume (P<0.05) and tumor weight (P<0.01) was markedly lower compared to the control group. 4-methyl- 3-nitro-benzoic acid demonstrated no effect on body weight change in mice. Conclusions: 4-methyl- 3-nitro-benzoic acid promises to be an effective new drug used in the treat-ment of malignant tumors.