Six constituents have been isolated from the hooks and stems of Uncaria sinensis. Five new 16-carboxy derivatives of oxindole alkaloids isopteropodic acid, pteropodic acid, mitraphyllic acid, isorhynchophyllic acid and rhynchophyllic acid, have been identified along with one known coumarin, scopoletin. Their structures were deduced on the basis of spectroscopic evidence and chemical correlations. The structure and relative stereochemistry of isorhynchophyllic acid were confirmed by X-ray crystallographic analysis. © 1993.