Recently, the herbal extract of Hibiscus sabdariffa was shown to have multiple bioactive effects, including anti-atherosclerosis. On the basis of this, we aimed to examine whether the polyphenolic isolate of H. sabdariffa (HPI) could protect high-glucose-treated vascular smooth muscle cell (VSMC) and its putative transduction signals. Results showed that HPI dose- and time-dependently reduced the high-glucose-stimulated cell proliferation and migration. HPI suppressed the proliferating cell nuclear antigen (PCNA) level and matrix metalloproteinase (MMP)-2 activation. In addition, the expressions of connective tissue growth factor (CTGF) and receptor of advanced glycation end product (RAGE) enhanced by high glucose were prominently suppressed by HPI. The proliferation signal mediated by high glucose was demonstrated via CTGF/RAGE, while MMP-2 was regulated by CTGF but not RAGE. Conclusively, the results suggest that HPI potentially can be a promising adjuvant herbal therapy for diabetic patients.