To investigate the coronary venous system (CVS) and its spatial relationship with coronary arteries by using 256-slice computed tomography (CT). One hundred one patients underwent coronary CT angiography by using a 256-slice CT. In each patient, the CVS and its spatial relationship with coronary arteries were analyzed. We measured the diameters and angulations of the coronary sinus (CS), great cardiac vein, anterior interventricular vein (AIV), left marginal vein, posterior vein of the left ventricle (PVLV), and posterior interventricular vein (PIV), and the distances, respectively, from the CS ostium and from the crossing point to the ostium of corresponding tributaries. The following 5 pairs of veins and arteries had a higher frequency of intersecting compared with others: the CS/great cardiac vein and the left circumflex coronary artery (97.1%), the AIV and the diagonal or ramus branch (92.1%), the PIV and the posterior branch of left ventricle artery (88.1%), the left marginal vein and the circumflex or circumflex marginal (73.9%), and the PVLV and the circumflex or circumflex marginal (31.6%). The other 2 pairs had a higher frequency of running parallel to each other: the AIV and the left anterior descending artery (76.2%) and the PIV and the posterior descending artery (54.4%). Most tributaries were lateral to their corresponding arteries at the crossing point except for the AIV. For the PVLV and PIV, the distances from the crossing point to the ostium of corresponding veins when the veins were lateral to the arteries were smaller than those when the veins were medial to the arteries (P < 0.05). The CVS and its anatomical relationship with the coronary arterial system can be examined with details by using a 256-slice CT, which has important clinical implications.