A new alkaloid, gardquinolone [1], was isolated from the leaves of Gardneria nutans. Its unique structure, having a 4-quinolone nucleus corresponding to the monoterpenoid indole alkaloids, was determined by spectroscopic analysis and chemical transformation from the indole alkaloid, gardnerine [2], which is a plausible biogenetic precursor of 1. Our comprehensive research on the chemical components of Gardneria (Loganiaceae) has clarified that this genus is a rich source of monoterpenoid indole alkaloids possessing a sarpagine skeleton (2). Starting with the Gardneria alkaloids, we have carried out a number of chemical transformations leading to many skeletal types of indole alkaloids (2-4). Reinvestigation of the alkaloidal constituents in the leaves of Gardneria nutans Sieb. et Zucc. (5) has resulted in the isolation of a new type of alkaloid, which we wish to report in this paper.