Objective: To investigate the efficiency of spectral computed tomography (CT) optimal monochromatic images in improving imaging quality of liver vessels. Materials and Methods: The imaging data of 35 patients with abdominal CT angiography were retrospectively analyzed. Hepatic arteries, portal veins, and hepatic veins were reconstructed with mixed energy (quality check, QC), 70 keV and optimal monochromatic mode. Comparative parameters were analyzed including CT value, image noise (IN), contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and subjective qualitative analysis. Results: The optimal monochromatic value for assessment of the common hepatic artery, portal vein, and hepatic vein ranged between 49 keV and 53 keV, with a mean of 51 keV. There were statistically significant differences (p < 0.001) among the optimal monochromatic, 70 keV and QC images with regards to the hepatic vascular CT value, IN, CNR, SNR, and subjective qualitative score. CNR of the common hepatic artery in the optimal monochromatic, 70 keV and QC groups was 24.6 +/- 10.9, 18.1 +/- 8.3, and 11.6 +/- 4.6, respectively (p < 0.001) with subjective scores of 4.7 +/- 0.2, 4.0 +/- 0.3, and 3.6 +/- 0.4, respectively (p < 0.001). CNR of the hepatic portal vein was 6.9 +/- 2.7, 4.3 +/- 1.9, and 3.0 +/- 2.1, respectively (p < 0.001) with subjective scores of 4.5 +/- 0.3, 3.9 +/- 0.4, and 3.3 +/- 0.3, respectively (p < 0.001). CNR of the hepatic vein was 5.7 +/- 2.3, 4.2 +/- 1.9, and 2.7 +/- 1.4, respectively with subjective scores of 4.3 +/- 0.3, 3.8 +/- 0.4, and 3.2 +/- 0.3, respectively (p < 0.001). Conclusion: Optimal monochromatic images can lead to improvement in the imaging parameters and optimization of the image quality of the common hepatic artery, hepatic portal vein and hepatic vein compared with conventional mixed kV and with 70 keV datasets.