To evaluate the effect of different treatment plans for whole-pelvic irradiation on small-bowel volumes (SBVs) in patients with gynecologic malignancies, 40 patients were enrolled in this study. Computed tomography (CT) simulations were performed, and the small bowel of each patient was outlined manually. Treatment plans with equal-weighted (EW) and non-equal-weighted (NEW) (70% in bilateral directions) techniques of four-field and intensity-modulated radiation therapy (IMRT) were performed. The V10–V100 represented the volume (cm3) at different levels of the prescribed doses (10–100%). The V10–V100 was compared among the different treatment planning techniques, and patients who were suitable for IMRT or NEW were identified. IMRT and NEW significantly reduced the V50–V100 and V40–V60 levels compared with EW, respectively. NEW caused a significant reduction in the V30–V60 levels in patients with a BMI ≥26 kg/m2. Patients with IMRT demonstrated lower V70–V100 levels compared with those with NEW. In patients with a BMI ≥26 kg/m2 or an age ≥55 years, lower V20–V50 levels were noted using NEW compared with IMRT. Treatment planning with larger weighting in the bilateral directions in four-field radiotherapy reduces the low-dose SBV in patients with gynecologic malignancies, especially in those with a high BMI or the elderly. IMRT effectively reduces high-dose SBV, especially in patients with a low BMI.