Objective To provide a preparation method for andrographolide-modified compound J6 and to verify its antitumor effects.Methods Andrographolide was mixed with propionic anhydride in a ratio of ≤72 mg∶5 mL. At 120~180 ℃, andrographolide hydroxyl groups at positions 3, 14 and 19 were modified into propionyl groups to obtain andrographolide-modified compound J6 , which was structurally characterized by ¹³C NMR and ¹H NMR. CCK8 assay was used to detect the effects of J6 on the proliferation of gastric cancer MKN45 cells, renal cancer 786O cells and melanoma A375 cells, and the effects of J6 on cell proliferation was compared with that of andrographolide.Results The results of CCK8 showed that andrographolide-modified compound J6 inhibited the proliferation of gastric cancer, renal cancer and melanoma cells in a time- and concentration-dependent manner. Compared with andrographolide, J6 showed a more significant inhibitory effect on tumor.Conclusion In this study, an andrographolide-modified compound J6 was synthesized. J6 can exert more efficient inhibition on the growth of gastric cancer MKN45 cells, kidney cancer 786O cells and melanoma A375 cells in a lower dose range, providing a new idea for the development of antitumor drugs.