Objective Several studies have examined the relationships between dietary potassium and sodium and hypertension, but few have evaluated the association between serum potassium or sodium and risk of incident hypertension. We therefore investigated the associations between serum potassium and sodium and risk of incident hypertension in a Chinese community-based population. Methods A total of 839 normotensive individuals without cardiovascular disease from the Chinese Multi-Provincial Cohort Study who took part in the baseline examination in 2007-2008 and the follow-up survey in 2012-2013 were included in this study. Odds ratios (OR) and 95% confidence intervals (95% CI) for baseline serum potassium and sodium in relation to the risk of new-onset hypertension were evaluated using multivariate logistic regression models. Results During five years of follow-up, 218 (26.0%) individuals progressed to hypertension. Logistic regression adjusting for multiple confounders showed that every 1 mEq/L increment in baseline serum potassium level was associated with a 75% increased risk of hypertension (OR: 1.75; 95% CI: 1.01-3.04; P = 0.04). Compared with adults with serum potassium level of 4.20-4.79 mEq/L, adults with level >= 4.80 mEq/L had an 84% increased risk of hypertension (OR: 1.84; 95% CI: 1.14-2.96; P = 0.01). There was no significant association between serum sodium and risk of hypertension (OR: 0.96; 95% CI: 0.89-1.04; P = 0.33). Conclusions Baseline serum potassium level, but not baseline serum sodium level, was positively related to the risk of incident hypertension in the Chinese population.