In our previous study, we found that LJNK showed potent aminopeptidase N (APN)-inhibitory activity. In the current study, we further evaluated the antitumor effects of LJNK both in vitro and in vivo. Enzyme experiments showed that LJNK showed better inhibitory activity than bestatin against APN both from human carcinoma cells’ surface and from porcine kidney microsomes. In addition, LJNK could suppress rat aortic ring microvessel growth and HUVEC tubular structure formation, which showed its stronger antiangiogenesis effects than bestatin. [(3-[4,5-Dimethyl-2-thiazolyl]-2,5-diphenyl-2H-tetrazolium bromide)] assay and clonogenic assay showed that LJNK suppressed cancer cell growth both in the short and the long term. Mice bearing H22 transplantation tumor proved its antitumor effects in vivo. Annexin V-fluorescein isothiocyanate/propidium iodide assay showed that LJNK could induce 28.1% PLC/PRF/5 cell apoptosis and the apoptotic pathway was probably identified by western blot. The above-mentioned results suggested that LJNK inhibited cell proliferation and angiogenesis, and induced apoptosis by decreasing APN activity.