T. dealbata is not only an ornamental plant due to its beautiful purple flowers blooming in the summer, but is also a powerful aquatic plant for wetland sewage treatment due to its luxuriant roots. Our present study found the allelopathic potential of T. dealbata on the growth inhibition of cyanobacteria. Both the M. aeruginosa and A. flos-aquae experiments showed a concentration-dependent manner. The maximal inhibiting ratios reached 92.7% in M. aeruginosa and 85.2% in A. flos-aquae, respectively, which indicated that T. dealbata is a powerful allelopathic macrophyte on cyanobacterial blooming.