Since the research on antioxidants provides theoretical information for the medicinal development, and supplies some in vitro methods for quick-optimizing drugs, it attracts more scientific attention from bioorganic and medicinal chemists. In addition to the traditional O-H bond-type antioxidant, carbazole and its related tricyclic amines (Ar2NHs), in which N-H bond functioned as the antioxidant, have attracted much research attention because Ar2NHs have always been the central structure in many currently used drugs. Thus, the investigation on the structure-activity relationship (SAR) between Ar2NHs and their free-radical-scavenging capacities in detail will benefit the development of novel radical-scavenging drugs containing Ar2NHs as the central structure. Therefore, carbazole (CazNH) and its structural analogues including phenoxazine (PozNH), phenothiazine (PtzNH), iminostilbene (IsbNH) together with diphenylamine (DpaNH) were applied to protect human erythrocytes against 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH)-induced hemolysis in vitro. By introducing the chemical kinetic formula related to free radical reaction, namely, the quantitative relationship between inhibition period (tinh) and the concentration of antioxidant (AH), tinh=(n/Ri)[AH], into AAPH-induced hemolysis, the values of stoichiometric factor (n) of Ar2NHs indicated that the free-radical-scavenging sequence of Ar2NHs is PozNH>DpaNH>CazNH>IsbNH>PtzNH >alpha-tocopherol (TocH). Another aim of this work was to investigate the antioxidative effect of Ar2NHs used together with other antioxidants including Trolox (TroH), VC, L-ascorbyl-6-laurate (VC-12), and TocH. The obtained data revealed that n value of PozNH when used together with all the other antioxidants decreases, whereas, n values of CazNH, DpaNH, IsbNH, and PtzNH when used in combination with TroH increase, demonstrating that two different interaction styles existed in the case of Ar(2)NHs used with other antioxidants. These findings may be useful for the development of agents for various ROS-mediated diseases in vivo.