Type 2 diabetes mellitus (DM) carries an increased risk for cardiovascular complications. The brachial-ankle pulse wave velocity (baPWV) is an index for early atherosclerotic changes. Recently, the effect of altered blood rheology on atherosclerosis has received attention. Therefore, this study aimed to examine the association of hemorheological parameters with baPWV in patients with DM. In this cross-sectional study, we investigated the relationship between rheological parameters and baPWV in 323 control subjects (160 men and 163 women) and 382 patients with DM (170 men and 212 women). The participants with DM had higher whole blood viscosity (WBV) levels both at low shear rate (3 s(-1)) and at high shear rate (200 s(-1)) than those without DM. Different metabolic parameters were compared across WBV (3 s(-1)) quartiles. The mean values of baPWV gradually increased with WBV (3 s(-1)) quartiles. In addition, there was a positive correlation between baPWV and WBV 3 s(-1) in patients with DM after adjusting confounding factors (r = 0.285, p = 0.039). Stepwise multiple linear regression analysis further revealed that WBV (3 s(-1)) is a significant determinant for increased baPWV in DM (β = 0.184; p < 0.001). However, there were no association between WBV (3 s(-1)) and baPWV in control subjects. The findings showed that baPWV increased as WBV (3 s(-1)) elevated in DM. Moreover, WBV (3 s(-1)) is independently associated with baPWV even after adjusting other cardiovascular risk factors. Early detection of abnormal WBV levels at low shear rate should warrant for early search of undetected arterial stiffness in patients with DM.