Rationale and Objectives: The preoperative evaluation of tumor grading and angiogenesis has important clinical implications in the treatment and prognosis of patients with colorectal cancers (CRCs). The aim of the present study was to assess tumor perfusion with 256-slice computed tomography (CT) using whole-volume perfusion technology before surgery, and to investigate the differences in the perfusion parameters among tumor grades and the correlation between perfusion parameters and pathologic results in CRC. Materials and Methods: Thirty-seven patients with CRC confirmed by endoscopic pathology underwent whole-volume perfusion CT assessments with a 256-slice-CT and surgery. Quantitative values for blood flow, blood volume, and time to peak were determined using commercial software. After surgery, resected specimens were analyzed immunohistochemically with CD105 antibodies for the quantification of microvessel density (MVD). The difference in CT perfusion parameters and MVD among different tumor differentiation grades was evaluated by the Student-Newman-Keuls test. The Correlations between CT perfusion parameters and MVD were evaluated using the Pearson correlation analysis. Results: The mean blood flow was significantly different among well, moderately, and poorly differentiated group (61.17 +/- 17.97, 34.80 +/- 13.06, and 22.24 +/- 9.31 mL/minute/100 g, respectively; P < .05). The. blood volume in the well-differentiated group was significantly higher than that in the moderately differentiated group (33.96 +/- 24.81 vs. 16.93 +/- 5.73 mL/100 g; P = .002) and that in the poorly differentiated group (33.96 +/- 24.81 vs. 18.05 +/- 6.01 mL/100 g; P = .009). The time to peak in the poorly differentiated group was significantly longer than that in the well-differentiated group (27.81 +/- 11.95 vs. 17.60 +/- 8.53 seconds; P = .016) and that in-the moderately differentiated group (27.81 +/- 11.95 vs. 18.94 +/- 7.47 seconds; P = .028). There was no significant difference in the MVD among well moderately, and poorly differentiated groups (33.47 +/- 14.69, 28.89 +/- 11.82, and 29.89 +/- 11.02, respectively; P > .05). There was no significant correlation between CT perfusion parameters and MVD (r = 0.201, 0.295, and -0.178, respectively; P = .233, .076, and .292, respectively). Conclusions: CT whole-volume perfusion technology has the potential to evaluate pathologic differentiation grade of CRC before surgery. However, preoperative perfusion CT parameters do not reflect the MVD of CRC.