The purpose of this study was to compare the dose distribution of intensity-modulated radiotherapy (IMRT) in 7 and 5 fields as well as 3-D conformal radiotherapy (3D-CRT) plans for gastric cancer using dosimetric analysis. In 15 patients with gastric cancer after D1 resection, dosimetric parameters for IMRT (7 and 5 fields) and 3D-CRT were calculated with a total dose of 45 Gy (1.8 Gy/day). These parameters included the conformal index (CI), homogeneity index (HI), maximum dose spot for the planned target volume (PTV), dose-volume histogram (DVH) and dose distribution in the organs at risk (OAR), mean dose (Dmean), maximal dose (Dmax) in the spinal cord, percentage of the normal liver volume receiving more than 30 Gy (V30) and percentage of the normal kidney volume receiving more than 20 Gy (V20). IMRT (7 and 5 fields) and 3D-CRT achieved the PTV coverage. However, IMRT presented significantly higher CI and HI values and lower maximum dose spot distribution than 3D-CRT (P=0.001). For dose distribution of OAR, IMRT had a significantly lower Dmean and Dmax in spinal cord than 3D-CRT (P=0.009). There was no obvious difference in V30 of liver and V20 of kidney between IMRT and 3D-CRT, but 5-field IMRT showed lower Dmean in the normal liver than other two plans (P=0.001). IMRT revealed favorable tumor coverage as compared to 3D-CRT and IMRT plans. Specifically, 5-field IMRT plan was superior to 3D-CRT in protecting the spinal cord and liver, but this superiority was not observed in the kidney. Further studies are needed to compare differences among the three approaches.