Objective To determine the consistency of spectral CT parameters in advanced gastric cancer using different region of interests (ROIs) and their relationship with tumor micro-vessel density (MVD).Methods Thirty patients with histologically proven gastric cancer were prospectively enrolled.All the patients were examined using spectral-dual-phase-abdominal CT and treated successfully with radical surgery within 2 weeks after CT scanning.Two observers independently acquired iodine concentration(IC), normalized IC(nIC),and CT value at workstation using three different ROI protocols:10 mm2 circular ROI near tumor border where enhanced obviously,30 mm2 near the tumor center and the freehand outline ROI. The Data of the two observers were tested with interclass correlation coefficient (ICC) and Bland-Altman plot.The mean value of each parameter was documented as the final result.Differences of each group of ROI data were compared using ANOVA test. All the specimen were pathologically examined and MVD was counted. The relationship of each parameter to tumor MVD was analyzed by Pearson correlation. Results All of the IC,nIC and CT values obtained by the 2 observers using three ROI measurements were consistent well,and the ROI-outline had the highest ICC than that of smaller circular ROIs(ICC:0.991 to 0.997).The 95% differences confident interval of nIC-AP and nIC-VP using freehand outline ROI by two observers were-0.003 to 0.002 and -0.001 to 0.012, respectively. The outline-ROI method had better inter-observer accuracy. There were significant differences between the means of the all parameters with three ROI protocols (P<0.05). Values of ROI-10 mm2 were highest, while the values of ROI-outline were lowest (P<0.05).The mean counts of tumor MVD was(29.0±8.4)/high magnification.The nIC in venous phase(VP)had good correlations with intra-tumoral MVD, especially the ROI-outline (r=0.670, P<0.01), within different ROI measurements.Conclusions The different ROI selection in tumor has significant impact on the final CT parameters. Outlined ROI protocol improves inter-observer consistency and nIC-VP obtained by this method can indirectly reflect the condition of tumor angiogenesis.