Tomato powdery mildew, caused by Oidium neolycopersici , is a destructive fungal disease that damages almost all of the aerial parts of tomato, causing devastating losses in tomato production worldwide. WRKY transcription factors are key regulators of plant immunity, but the roles of ShWRKYs in wild tomato Solanum habrochaites LA1777 against O. neolycopersici still remain to be uncovered. Here, we show that ShWRKY81 is an important WRKY transcription factor from wild tomato Solanum habrochaites LA1777, contributing to plant resistance against O. neolycopersici . ShWRKY81 was isolated and identified to positively modulate tomato resistance against On -Lz. The transient overexpression of the ShWRKY81-GFP (green fluorescent protein) fusion protein in Nicotiana benthamiana cells revealed that ShWRKY81 was localized in the nucleus. ShWRKY81 responded differentially to abiotic and biotic stimuli, with ShWRKY81 mRNA accumulation in LA1777 seedlings upon On -Lz infection. The virus-induced gene silencing of ShWRKY81 led to host susceptibility to On -Lz in LA1777, and a loss of H 2 O 2 formation and hypersensitive response (HR) induction. Furthermore, the transcripts of ShWRKY81 were induced by salicylic acid (SA), and ShWRKY81- silenced LA1777 seedlings displayed decreased levels of the defense hormone SA and SA-dependent PRs gene expression upon On -Lz infection. Together, these results demonstrate that ShWRKY81 acts as a positive player in tomato powdery mildew resistance.