Vinca alkaloids (VAs) obtained from Catharanthus roseus (L.) G. Don have been employed in clinic owing to their antitumor effects. Toxicities of VAs are significantly different despite similar structures. However, the structure-toxicity relationships of VAs remain unclear. In view of this, Tetrahymena thermophila BF5 (T.t. BF5) was used to evaluate the toxic effects of VAs by microcalorimetry, which could dynamically monitor the growth of T.t. BF5. The IC10 results showed the relative toxicity of VAs was vincristine (105.0 +/- 16.3 mu gmL(-1))>vindesine (135.1 +/- 5.1 mu gmL(-1))>vinblastine (215.5 +/- 4.7 mu mL(-1))>vinorelbine (314.2 +/- 15.9 mu gmL(-1)). Analysis of structure-toxicity relationships indicated that acylamide at C3 position and hydroxyl at C4 position might contribute to more toxicity. A long conjugation effect appearing in VAs could increase the toxicity when the N1 position was substituted with formyl group. (C) 2017 Elsevier B.V. All rights reserved.