Objective To evaluate the diameter of segmental and sub-segmental pulmonary arteries of the right middle lobe using multislice spiral CT angiography. BR>Methods Two handred and fifty-four patients with no cardiac pulmonary diseases were performed with thoracic enhanced CT scans. Different methods for three-dimensional reconstruction imaging were selected in this investigation. The patients were divided into gender groups and three age groups of 20-40 year, 41-60 year, and 61-87 year. The diameter of segmental and sub-segmental pulmonary arteries of the middle right lobe on the MPR images were observed and measured. The obtained data were statistically analyzed. Results There were significant differences of the diameter of pulmonary arteries between the male and the female and among age groups. Different reconstruction methods had their own advantages. MPR reconstruction appeared better as it provided a more accurate evaluation for segmental and sub-segmental pulmonary arteries. Conclusion The imaging of multislice spiral CT can properly evaluate the diameter of segmental and sub-segmental pulmonary arteries of the right middle lobe and provide reference data for clinical diagnosis. BR>