Objective To observe the preventive effect of dexmedetomidine on penile erection(PE) after general anesthesia induction and urinary bladder irritation during recovery(UBIR) with urethral catheterization in male patients.Methods A total of 1000 male patients with ASA grade Ⅰ ～ Ⅱ were randomly divided into control group(group C) and dexmedetomidine group (group D,n =500).Dexmedetomidine (1 μg/kg) was intravenous pumped in group D and saline was given in group C 15 minutes before anesthesia induction.Both groups started catheterization within 10 minutes after endotracheal intubation.The incidence and grade of PE before infusion(To),before induction(T1),before catheterization(T2) and during catheterization (T3) were observed.The degree and extent of UBIR were observed and recorded.Results The incidence and grade of PE at T3 time-point in group C were highest (Compared with T2 and other time-points,P ＜ 0.05),but there was no statistically differences in incidence and grade of PE in group D between at T3 and T2time points (P ＞ 0.05).The incidence of PE at T2 and T3 time-points were 4.0％ and 5.6％ in group D,which was significantly lower than those in group C (15.4％,77.8％,P＜0.05).The incidence of PE at grade 1,2 and3 was 4.4％,1.0％ and0.2％ respectively in group D,which was significantly lower than those in group C (62.6％,11.4％,3.8％,P ＜ 0.05).The incidence of UBIR was significantly lower (28.4％ vs 63.0％,P ＜ 0.05),among which the incidence of UBIR at grade 1,2 and 3 were 15.6％,10.4％ and 2.4％,which was significantly lower in group D than those in group C (22.0％,21.0％,20.0％,P ＜ 0.05).Conclusion 1μg/kg dexmedetomidine pumped before anesthesia induction could prevent the occurrence of PE during catheterization and UBIR,which can improve patients' comfort.