The aim of this study was to evaluate the influence of clinic and ambulatory blood pressure (BP) on the occurrence of new‐onset atrial fibrillation (AF) in treated hypertensive patients. We studied 2135 sequential treated hypertensive patients aged >40 years. During the follow‐up (mean 9.7 years, range 0.4–20 years), 116 events (new‐onset AF) occurred. In univariate analysis, clinic, daytime, nighttime, and 24‐h systolic BP were all significantly associated with increased risk of new‐onset AF, that is, hazard ratio (95% confidence interval) per 10 mm Hg increment 1.22 (1.11–1.35), 1.36 (1.21–1.53), 1.42 (1.29–1.57), and 1.42 (1.26–1.60), respectively. After adjustment for various covariates in multivariate analysis, clinic systolic BP was no longer associated with increased risk of new‐onset AF, whereas daytime, nighttime, and 24‐h systolic BP remained significantly associated with outcome, that is, hazard ratio (95% confidence interval) per 10 mm Hg increment 1.09 (0.97–1.23), 1.23 (1.10–1.39), 1.16 (1.03–1.31), and 1.22 (1.06–1.40), respectively. Daytime, nighttime, and 24‐h systolic BP are superior to clinic systolic BP in predicting new‐onset AF in treated hypertensive patients. Future studies are needed to evaluate whether a better control of ambulatory BP might be helpful in reducing the occurrence of new‐onset AF.