A mite damage was observed in spinach (Spinacia oleracea L.) under organic culture greenhouses. The mite was identified as Tyrophagus similis Volgin, 1949. It was very difficult for the farmers to diagnose the mite damage because of its tiny size about 0.5 nm in length. And the symptom was not clear at the early growth stage of the spinach because the mite mainly attack the very young leaves. In this study, we first report the spinach damages by T. similis in Korea. Informations on the mite morphology and the spinach damage symptoms are provided for the diagnosis.