Objective: To select the better method for the examination of functional outlet obstruction, the defecography with thickened barium (DTB) and the defecography with barium suspension (DBS)were compared and evaluated objectively. Methods：The comparison of DBS and DTB were carried out on the same day in 25 cases of constipation. Results: The average internal rectal diameter of DTB was 1.16cm larger than that of DBS. The average rectal volume of DTB was 2.2 times as large as of DBS. In 24 abnormal cases detected, the blocking and inlaying of barium were all revealed by the DTB and little barium remained in only 2 cases by the DBS. The average time of defecating with DTB were 9s, and with DBS were 2.5s. The capability of revealing the cause of obstruction at outlet were better in 14 DTB cases and better in 6 DBS cases. Conclusion: For the examination of functional outlet obstruction, the DTB is better than the DBS. The revealing quality can be improved if little concentrated barium suspension is injected before the thickened barium.