In May 2017, a new virus-like disease was observed on Lagerstroemia indica in Hangzhou, Zhejiang province, China. Symptoms observed included patches of vein clearing and chlorosis on Lagerstroemia indica leaves. A survey in the region indicated that more than 98% (n=1 485) of Lagerstroemia indica plants showed similar symptoms. To determine the causal agent, a small RNA (sRNA) library was constructed using symptomatic Lagerstroemia indica leaf tissue and sequenced. Based on the results of the Illumina Hiseq next-generation sequencing, reverse-transcription polymerase chain reaction, rapid amplification of cDNA ends, DNA sequencing and pathogenicity test, the causal agent was identified as Watermelon mosaic virus (WMV). This is thought to be the first report of WMV infecting a woody host. Notably, WMV-Li was also detected infecting Luffa cylindrica [L. aegyptiaca] with typical symptoms of vein clearing in a subsequent survey.