Objective: To investigate the enhancement basis and the mechanisms of solitary pulmonary nodules (SPNs) by comparing the differences in microvascular structure between benign and malignant lesions. Methods: Dynamic contrast-enhanced CT scan was performed on 53 patients with SPNs (diameter＜3 cm, 38 peripheral lung cancers, 5 hamartomas, 10 inflammatory lesions) using a Siemens Plus S or a Marconi MX8000 multi-slices spiral CT scanner. The time-attenuation curves were interpreted. The microvascular density (MVD) and the continuity of the microvessels basemental membrane in the dissected specimens were observed with the ABC (avidin-biotin-complex) immuno-histochemical method in all patients. Results :The CT enhancement values of lung cancer (49.05± 16.08 HU) and inflammatory lesions (49.59±21.30 HU) were significantly higher than those of hamartoma (8.98±4.56 HU) (t=7.48,P＜0. 05; t=8.35, P＜0. 05). But the enhancement of lung cancer was similar to that of inflammatory lesions (t= 0. 76, P＞ 0. 05). The time-attenuation curve of inflammatory lesions tended to increase faster and reached a higher peak compared to the lung cancer, and both of them maintained a high plateau after crossing. The hamartoma showed a slight increase in the time-attenuation curve and demonstrated a lowplateau curve. The MVD of SPNs was positively correlated with CT enhancement (r=0. 8051). The microvascular counts of peripheral lung cancer (48.45± 10.09) and inflammatory lesions (49. 60±19. 94)were significantly higher than those of hamartoma (8.70±7.30) (t=11. 64, P＜0. 001; t=6. 09, P＜0. 001), but no significant difference was found between lung cancer and inflammatory lesions (t=- 0. 26,P=0. 799). There was no difference in the continuity of basement membrane between nodules with an enhancement less than 30 HU and those with an enhancement higher than 30HU (x2= 3.13, P＞0. 05 ).Conclusion: The microvascular counts mainly contribute to the enhancement value of SPNs. The basement membrane is not related to nodule enhancement, but it might influence the pattern of the time-attenuation curve.