Little information on the relationship between blood rheology and atherosclerosis indicators in obese patients is available. We examined blood rheology as assessed by the blood passage time (BPT) with the microchannel method in 109 obese patients. BPT was correlated well with the extent of each metabolic syndrome component. A multivariate regression analysis revealed that the independent contributors to BPT were pulse-wave velocity, an index of arterial stiffness, body mass index and red blood cell. Furthermore, weight reduction intervention significantly decreased BPT. Assessment of rheology may be associated with pulse-wave velocity, and useful to manage obese patients.