Background: Beta blocker (BB) is one of the most important drugs for heart failure (HF). The effect of BB is related to decrease in heart rate (HR). However, among HF patient with atrial fibrillation (AF), the relationship between BB and decrease in HR is unknown. Method and result: We enrolled consecutive 631 patients were admitted to our hospital for acute decompensated HF in 2015. 150 patients with AF both on admission and discharge was selected. 62 (41.3%) of whom received up-titration of BB in hospitalization. 127 (84.6%) of whom decreased HR on discharge comparing with on admission. The incidence of all cause death and HF re-hospitalization was not significant different between up-titration of BB group and without up-titration group (48.3% vs. 56.8%, P=0.71). The incidence of all cause death and HF re-hospitalization was significant lower in decrease in HR group than in without decrease in HR group (50.3% vs. 69.5%, P?0.01). We analyzed up-titration of BB group and without up-titration group, respectively. The incidence of all cause death and HF re-hospitalization in up-titration of BB group was significant lower in decrease in HR group than in without decrease in HR group (45.6% vs. 80.0%, P=0.03). And similar result was obtained from without up-titration of BB group (54.2% vs. 66.6%, P=0.02). Conclusion: Decrease in HR may have a better prognosis than up-titration of beta blocker for acute decompensated HF with AF.