It remains unclear whether ambulatory blood pressure variability (BPV) contributes toward day-by-day BPV, despite the fact that not only day-by-day but also ambulatory BPV is reported to be a risk factor for type 2 diabetes patients. This study aimed to determine the association between day-by-day BPV and ambulatory BPV, which is especially distinguished between diurnal and nocturnal BPV, in type 2 diabetes patients. Day-by-day and ambulatory BPV were assessed in 30 type 2 diabetes patients (aged 54±15 years; 87% men; glycated hemoglobin: 9.1±1.9%) in inpatient settings. Day-by-day systolic BPV was correlated significantly with diurnal systolic BPV (r=0.426, P=0.019), but not nocturnal systolic BPV (r=0.175, P=0.354). Multiple regression analysis showed that diurnal systolic BPV and diurnal mean systolic blood pressure were associated independently with day-by-day systolic BPV. With respect to type 2 diabetes, these findings suggest that day-by-day BPV is reflected in diurnal BPV rather than nocturnal BPV.