Unusual mushrooms were observed in the greenhouses of vegetables Chinese chive, cucumber, melon and Korean dandelion in four locations of Korea in 2012. The mushrooms usually grew with the vegetables cultivated on beds in the greenhouses. Occurrence aspects of the mushrooms in the greenhouses and effect of the mushrooms on growth and quality of the vegetables were investigated. Mushroom samples were collected from the beds in the greenhouses and identified based on their morphological characteristics. The mushroom samples collected from the greenhouse of Chinese chive were identified as Coprinus aokii, those from the greenhouse of cucumber as Cristinia eichleri and Coprinus sp., those from the greenhouse of melon as Leucocoprinus cretaceous, Panaeolus fimicola and Conocybe sp., and those from the greenhouse of Korean dandelion as Conocybe rickenii f. tetrasporique. Out of the seven mushrooms identified, L. cretaceus, C. rickenii and C. eichleri were first found in Korea. The investigation results revealed that the mushrooms were originated from compost or soil used in the beds, and showed that C. aokii caused sooty mold on leaves of Chinese chive, and C. rickenii f. tetrasporique hindered growth of Korean dandelion and caused sooty mold on leaves of the plant. The other mushrooms had no effect on growth and quality of the vegetables.