Inhibition of histone deacetylase (HDAC) results in growth arrest, differentiation, and apoptosis in nearly all tumor cell lines, promoting HDACs as promising targets for antitumor therapy. In our previous study we developed a novel series of 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid derivatives as HDAC inhibitors (HDACi), among which compound 7d exhibited promising HDAC8 inhibitory and antiproliferative activities. Herein, we report the design and development of a new class of tetrahydroisoquinoline-bearing hydroxamic acid analogues as potential HDACi and anticancer agents. In vitro biological evaluation of these compounds showed improved HDAC8 inhibition (compounds 31a and 31b exhibited mid-nM IC(50) values against HDAC8) and potent growth inhibition in multiple tumor cell lines. Most importantly, compounds 25e, 34a, and 34b exhibited excellent in vivo anticancer activities in a human breast carcinoma (MDA-MB-231) xenograft model compared with suberoylanilide hydroxamic acid (SAHA), an approved HDACi. Collectively, our results indicate that tetrahydroisoquinoline bearing a hydroxamic acid is an excellent template to develop novel HDACi as potential anticancer agents.