In this study, narciprimine and arolycoricidine were isolated from G. rizehensis Stern (Amaryllidaceae). The structures of the alkaloids were elucidated by spectroscopic methods (1D NMR, EI-MS). Due to the previous reports on anti-cancer activity of this group of alkaloids, we investigated their effects on DNA topoisomerase reactions, which are known as the cellular targets of a number of chemotherapeutical drugs. The results revealed that arolycoricidine and narciprimine were effective in both type I and type II DNA topoisomerase reactions in a dose-dependent manner. Topoisomerase-interfering ability of these alkaloids partially correlated with cytostaticity assays, using HeLa (cervix adenocarcinoma), MCF7 (breast adenocarcinoma) and A431 (skin epidermoid carcinoma) cells. Our results are discussed in relation to the potential significance of these alkaloids in the course of drug-development studies.