BACKGROUND: Dietary Approaches to Stop Hypertension (DASH)-Sodium trial showed that dietary sodium and potassium affect blood pressure (BP). We aimed to investigate whether dietary sodium and potassium affect short-term BP variability (BPV) in addition to BP. METHODS: A total of 343 participants from the DASH-Sodium trial (age 48.4 ± 9.7, 42.5% men) and 323 individuals from the Jackson Heart Study (JHS) (age 56.7 ± 11.2, 30.7% men) with satisfactory ambulatory BP monitoring records and 24-h urine collection were included. Average real variability (ARV) was calculated as a measure of short-term BPV. RESULTS: By estimating dietary intake from urinary excretion, we observed that higher urinary sodium-to-potassium ratio was significantly associated with higher diastolic ARV in both studies. Among the DASH-Sodium trial, potassium-rich DASH diet alone had insignificant effect on both systolic (-0.1 ± 1.7 mmHg, P = 0.343) or diastolic ARV (-0.2 ± 1.5 mmHg, P = 0.164), whereas combined DASH diet and low sodium intake significantly reduced both systolic (8.5 ± 1.6 vs. 8.9 ± 1.7 mmHg, P = 0.032) and diastolic ARV (7.5 ± 1.5 vs. 7.8 ± 1.6 mmHg, P = 0.025) as compared with control diet and high sodium intake. As the reduction of systolic ARV was majorly derived from the change of mean SBP, diastolic ARV was significantly determined by urinary sodium-to-potassium ratio (β coefficient ± standard error: 0.012 ± 0.004; P = 0.006) after adjusting for age, sex, smoking, mean DBP, BMI, and race. CONCLUSION: Dietary sodium and potassium can jointly modulate short-term BPV in addition to BP. Combined DASH diet and low sodium intake may reduce systolic and diastolic ARV via different mechanisms.