ABSTRACT In this study, it was aimed to determine the Kc of tomato, eggplant, pepper and cucumber grown in two consecutive seasons in a year in a common type of plastic greenhouse, using the reference (grass) (ETo) and crop evapotranspiration (ETc) values measured directly in lysimeters. The study was carried out at drainage-type lysimeters placed in the greenhouse, with three replications for each crop and grass at Akdeniz University, Antalya, Turkey, from 2019 to 2020. Seasonal ETo values varied between 206.0 and 329.1 mm, while seasonal ETc values of crops varied between 243.6 and 529.3 mm for growing seasons ranging from 105 to 137 days. The crop coefficient (Kc) of the tomato, eggplant, pepper and cucumber crops under greenhouse conditions were between 0.4 and 0.6 for the initial stage (Kc ini); for maximum Kc values (mid-season stage) (Kc mid) between 1.4 and 1.8 in spring and 1.6–1.9 in fall; for the end-of-season stage (Kc end) it varied between 1.1 and 1.8 in spring and 0.7–1.4 in fall. It was concluded that the Kc values were higher due to the fact that the ground cover development and crop architecture changed significantly in the greenhouse compared to the field conditions.