OBJECTIVE To study the correlation between in vitro release and in vivo absorption of captopril delayed-onset, sustained release tablets.METHODS The in vitro release characteristics of captopril delayed-onset, sustained release tablet were evaluated at 0.1 mol·L-1 hydrochloric acid medium. The results were compared with that of the common delayed tablet. The oral administration absorption in vivo was tested in beagle dogs with a single-dose, crossover study under fasting conditions, comparing the delayed-onset, sustained release tablets (CDSR) and common sustained release tablets(CSR). The fractions absorbed were calculated by the Wagner-Nelson method. The captopril concentration in plasma was determined by a pre-column derivation HPLC with a solid phase extraction. RESULTS The captopril concentration in plasma was not detected until 2 h after the oral administration, and the peak blood level occurred in 3-5 h after an oral administration, in vitro release started at 3.5 h, the accumulate release percent was about 10% at 5 h,the maximum release was reached in 8-10 h,for the delayed-onset, sustained release tablets. While the captopril concentration was detected at 0.5 h after the oral administration, and the peak blood level occurred in 1-3 h after the oral administration, the accumulate release percent in vitro was about 20% at 1 h, for the common delayed tablets. CONCLUSION There are some correlation between release in vitro and absorption of the delayed-onset in vivo , sustained release tablets, and the remarkable lag time is observed,compared with the common delayed tablets.