Purpose : The purpose of this study was to evaluate the utility of two-phase dynamic CT, early and equilibrium pahse, in the preoperative staging of rectal cancers. Materials and Methods : We performed incremental dynamic CT after rectal infusion of water in 34 patients with pathologically proved rectal cancers. Two-phase dynamic CT findings were prospectively analyzed and correlated with surgical and histopathologic findings. A total of 150 mlof nonionic contrast medium was intravenously administered with a power injector at a flow rate of 5 ml/sec for 30 sec, and two-phase images were obtained at 30 sec(early phase) and 2 min (equilibrium phase) after bolus injection. Local tumor staging and regional lymph node were classified by TNM staging. Results : All 34 rectal cancers showed a moderate to marked enhancement in the early phase and homogeneous and prolonged enhancement of the entire lesion in the equilibrium phase. T-staging of primary tumors were 85.3%(29/34) in early phase and 70.6%(25/34) in equilibrium phase. The accuracy in determining the perirectal fat invasion of rectal cancer was 92%(23/25) in early phase, and 72%(18/25) in equilibrium phase. The sensitivity & specificity of the regional lymph node metastasis were 63.6% and 79.1% in early phase, and 54.5% and 65.2% in equilibrium phase, respectively. Conclusion : Early phase dynamic CT was more accurate for the preoperative staging of rectal cancer than that atequilibrium phase.