Objective: To detect the possible molecular mechanisms of the formation of vessels that encapsulated tumor clusters (VETC) and identify the relationship between vimentin protein expression in endothelial cells and contrast-enhanced ultrasound characters in VETC (+ ) hepatocellular carcinoma (HCC). Methods: A total of 64 paraffin embedded HCC tissue samples were collected, all of which the tumor diameters were between 2 cm and 5 cm measured by the preoperative ultrasound. Immunohistochemistry staining for CD34 was used to detect the formation of VETC and the expressions of angiopoietin-2 (Ang-2) and vimentin were also determined. Human umbilical vein endothelial cells (HUVECs) were treated with 150 ng/ml recombinant human Ang-2 protein (rhAng-2) at various times and the protein expression of vimentin was detected by western blot assay. The contrast-enhanced ultrasound characters were also analyzed in both VETC (+ ) and VETC (-) HCC. Results: Tumor clusters encapsulated by vessels to form cobweb-like networks, which were identified as VETC phenotype, were observed in 27 HCC tissues (42.18%). In VETC (+ ) HCC tissues, Ang-2 was overexpressed in tumor cells and endothelial cells while vimentin was only upregulated in endothelial cells. With the treatment of 150 ng/ml rhAng-2 protein, the expression of vimentin in HUVECs was 0.878±0.102 and 0.918±0.092 at 12 h and 36 h, significantly upregulated when compared to the 0.322±0.061 at 6 h (P<0.01). In contrast-enhanced ultrasound, a crack and tendon-like filling character was observed in VETC (+ ) HCC during the arterial-phase, while the large scale and diffuse-like filling character was observed in VETC (-) HCC. The filling time of unit diameter in VETC (+ ) HCC was (3.95±0.22)s, significantly longer than (2.28±0.27)s of VETC (-) HCC (P<0.01). Conclusions The overexpressions of Ang-2 and vimentin are positively correlated with the formation of VETC and considered as potential therapeutic targets of VETC (+ ) HCC. The crack and tendon-like filling characters in arterial-phase of contrast-enhanced ultrasound indicates the VETC (+ ) HCC.