The purpose of this study was to compare the effects of miso and sodium chloride (NaCl) on blood pressure in both sexes of Dahl and SD rats. The systolic and diastolic blood pressures (SBP/DBP) were measured at 2, 4, 8 and 12 weeks of treatment with a miso diet including 2.3% NaCl, a high-sodium diet including 2.3% or 1.9% NaCl, or a normal diet including 0.3% NaCl (MF diet; Oriental Yeast Co., Tokyo, Japan). The rats were autopsied after 12 weeks on a diet. DBP in male Dahl rats was significantly increased by the 2.3% NaCl diet as compared with that in the MF group (p<0.01) or miso group (p<0.05) from 4 weeks of treatment. Thereafter, SBP and DBP in both the high NaCl groups were significantly increased when compared with the MF or miso group. SBP in female Dahl rats on 2.3% NaCl was significantly increased from 8 weeks after treatment. Nephropathy was observed in both sexes of Dahl rats but not SD rats. These results show that blood pressure was not increased by the miso diet.