Adopting indoor inhibitory on bacteriostatic activity and soaking seed potting experiment，
this paper investigated the control effect of Novonestmycin A on Rhizoctonia solani damping-off of watermelon.
Results of laboratory test indicated that Novonestmycin A had strong inhibitory effect on bacteriostatic activity
of Rhizoctonia solani，and its median inhibitory concentration was 1.726 0 μg · mL^-1. After being treated
with Novonestmycin A of 10 μg · mL^-1 concentration，the hyphae became morphologically irregular under
observation of optical microscope and scanning electron microscope. The results of pot experiment showed that
the control effect of soaking seed at the concentration of 4 000 μg · mL^-1 Novonestmycin on Rhizoctonia solani
damping-off of watermelon was 91.83%.