The antimicrobial peptide ToAMP4 was isolated from Taraxacum officinale Wigg. flowers. Bacterial-expressed ToAMP4 showed antifungal activity but was inactive against bacteria. In this study, Chlamydomonas reinhardtii was used to express a C-terminal hemagglutinin (HA) and 6 x His double tagged three repeats of ToAMP4 (3 x ToAMP4)and the 3 x ToAMP4-expressing cells were screened to express 3 x ToAMP4 stably following continuous passaging for six months. Finally, a yield of 0.32 % of total soluble protein was achieved for 3 x ToAMP4, which inhibits the growth of bacteria of both Gram-positive and Gram-negative at a minimum inhibitory concentration between 40 and 50 mu g/ml. C. reinhardtii-derived 3 x ToAMP4 maintained high stability in a wide range of temperature and pHs, tolerated to protease digestion at different extents and showed low hemolytic activity and cytotoxicity. Moreover, C. reinhardtii-expressed 3 x ToAMP4 effectively caused damage on the membrane of targeted bacterial cells. In conclusion, our data show that C. reinhardtii has the potential to be used as a platform for the production of bioactive ToAMP4.