In 2016, malformation and spotted wilt of leaves and fruit malformation were observed on cucumber (Cucumis sativus) in Kanagawa Prefecture. RT-PCR to amplify an RNA dependent RNA polymerase gene region of tospovirus and sequencing of the amplified fragment indicated highest identity with watermelon silver mottle orthotospovirus (WSMoV). The virus was isolated through two rounds of single lesion isolation and identified as WSMoV based on the nucleocapsid gene sequence. Cucumber plants inoculated with the isolated virus developed the same symptoms, and only WSMoV was shown to be present in RNA from symptomatic plants; nine other cucumber viruses were absent. This is the first report describing WSMoV symptoms on cucumber.