Objective   To explore the value of MR whole-body diffusion-weighted imaging (WB-DWI) in detecting pelvic lymph nodes.  Methods   30 cases of informed consent healthy men were selected randomly and 66 cases of pre-operative initial treatment men with pelvic malignant tumors were selected from June 2007 to November 2008 in our hospital. MR WB-DWI, T1-weighted imaging (T1WI) and T2-weighted imaging (T2WI) performed to observe the pelvic lymph nodes respectively. It was confirmed by surgery and pathology in patients with pelvic malignancies. Pelvic lymph nodes were counted and their size and ADC values were calculated according to their anatomical site.  Results   The normal pelvic lymph nodes could not show in the WB-DWI images. Contrast with T1+T2, the detection rate was 0.3% on WB-DWI sequence for pelvic lymph node whose short-axis diameter <0.5 cm, but the detection rate was 94.2% for the pelvic lymph node whose short-axis diameter ≥ 0.5 cm and <1.0 cm. The coincident rate of lymph node metastasis whose short-axis diameter ≥ 0.5cm was 89.3% between preoperative detection on WB-DWI and postoperative detection on pathology. There was no significant difference in the ADC values between metastatic and non-metastatic lymph nodes (P>0.05). Diagnostic time for the WB-DWI images was less than the time for the traditional MR images significantly (P<0.01).  Conclusions   The abnormal lymph nodes could be found quickly on WB-DWI sequence. There is a high value on WB-DWI sequence in determining pelvic lymph node involved by malignant tumors, and could be a relatively accurate method for preoperative evaluation.