Abstract The synthesis of a series of N-(2-chloroethyl)-N′-(9H-xanthen-9-yl)-N-nitrosoureas and N-(2-chloroethyl)-N′-(9H-thioxanthen-9-yl)-N-nitrosoureas is described. The title compounds were evaluated against NSCLCN6 L16 bronchial epidermoid carcinoma in vitro and some of them were found to be active. N-(2-chloroethyl)-N′-(2-methoxy-9H-xanthen-9- yl)-N-nitrosourea (8e) was active against leukemia P388 tumor system in mice.