Objective: The aim of this study was to determine an optimal slice thickness that was efficient in revealing lobulation of malignant solitary pulmonary nodules (SPNs) on multi-slice spiral computed tomography (MSCT) images preliminarily. Methods: Fifty patients with malignant SPNs (diameter ≤ 3 cm) underwent multidetector-row computed tomography of the chest in a single-breath-hold technique. The raw data were acquired with a collimation of 0.625 mm. Three sets of contiguous images were reconstructed with 1-, 2-, and 5-mm slice thickness, respectively. The lobulation sign of SPNs on the computed tomography (CT) images presented in 1-, 2-, and 5-mm slice thickness was compared. Using the 1-mm sections as the gold standard, an optimal slice thickness in revealing lobulation sign of SPNs was determined. Results: The 1-mm-thick images CT revealed 98 lobulations (25 with chord distance < 1 mm; 30 with chord distance 1-2 mm; 43 with chord distance > 2 mm) of 45 malignant SPNs. 18 lobulations with chord distance < 1 mm presented in 2-mm-thick sections were as same as those in 1-mm-thick sections. Statistically significant difference in lobulations number was found between that revealed in 2-mm-thick images and that in 1-mm-thick images (P = 0.023 < 0.05). 16 lobulations with chord distance < 1 mm presented in 5-mm-thick sections were as same as that in 1-mm-thick sections. There was statistically significant difference in lobulations number between that revealed in 5-mm-thick images and that in 1-mm-thick images (P = 0.004 < 0.05). The 24 lobulations with chord distance 1-2 mm presented in 2-mm-thick sections were as same as that in 1-mm-thick sections. No statistically significant difference in lobulations number were found between that revealed in 2-mm-thick images and that in 1-mm-thick images (P = 0.261 > 0.05). 13 lobulations with chord distance 1-2 mm presented in 5-mm-thick sections were as same as that in 1-mm-thick sections. There was statistically significant difference in lobulations number between that revealed in 5-mm-thick images and that in 1-mm-thick images (P = 0.003 < 0.05). 40 lobulations with chord distance ﹥2 mm presented in 2-mm-thick sections were as same as that in 1-mm-thick sections. No statistically significant difference in lobulations number was found between that revealed in 2-mm-thick images and that in 1-mm-thick images (P = 0.631 > 0.05). 36 lobulations with chord distance ﹥2 mm presented in 5-mm-thick sections were as same as that in 1-mm-thick sections. There was no statistically significant difference in lobulations number between that revealed in 5-mm-thick images and that in 1-mm-thick images (P = 0.264 > 0.05). Conclusion: It is suggested that the use of 1-mm slice thickness is suitable in revealing lobulations with chord distance < 1 mm. A 2-mm slice thickness is suggested to be used in revealing lobulations with chord distance 1-2 mm and 5-mm slice thickness to be used in revealing lobulations with chord distance > 2 mm.