OBJECTIVE To investigate the relative bioavailability and the correlation study on urapidil sustained release capsules between in vitro and in vivo.METHODS Urapidil concentration in plasma was detected by RP-HPLC after twenty four healthy male volunteers were treated with a single dose and multiple doses of oral urapidil sustained release capsules test and reference preparations.The data was calculated with 3P97 program.The results were analyzed by ANOVA and two one-side test. The dissolution of urapidil was determined in vitro according to CP(2000ed,partII).RESULTS The relative bioavailability of urapidil in the single dose treatment was (96.37±13.77)%AUC _0-t of urapidil test and reference preparations were (2347.6±493.2)ng·h·mL^-1 versus (2458.9±526.5) ng·h·mL^-1;t_maxwere (4.17±0.28) h versus (4.23±0.29)h;c_maxwere(325.6±40.3) ng·mL^-1 versus (322.0±75.5)ng·mL^-1.The relative bioavailability of urapidil in the multiple dose treatment was (99.99±16.24)%.AUC_0→tof urapidil test and reference preparation were (4513.1±1372.7)ng·h·mL^-1 versus (4549.7±1308.8)ng·h·mL^-1,t_maxwere(4.00±0.49)h(4.08±0.43)h,c_maxwere(544.5±147.1)ng·mL^-1 versus (565.7±146.8)ng·mL^-1,DF were (91.22±14.07)% versus (84.53±26.10)%.The dissolution of urapidil in the two preparations was 86.33% and 87.35% within 12h, respectively.CONCLUSION Bioequivalent evaluation of two preparations by two one side test and rank sum test showed that the two preparations were bioequivalent. There was a significant relationship between absorption in vivo and dissolution in vitro (P<0.05).