3-Oxo-7-hydroxy-3,7-secorhynchophylline (1), an oxindole alkaloid found in Uncaria attenuata, was prepared from isorhynchophylline (2), and two diastereomers ascribable to C7 of the natural and semi-synthetic 1 were separated by chiral column chromatography. The absolute configuration at C7 was elucidated by comparison of the CD spectra with those of the known oxytryptophan derivatives (8a and 8b). Further, the absolute configuration of some natural products having a 3-substituted-3-hydroxyoxindole moiety was deduced by utilizing the new CD spectral finding obtained in the present study.