A series of hydroxyurea derivatives have been synthesized and elucidated by means of FT-IR, ¹H-, ¹³C-NMR and MS. The exact stereostructures of representative compounds have been determined by X-ray crystal structure analysis. In the crystals, inversion dimers linked by pairs of N–H…O hydrogen bonds occurred, and further N–H…O links led to chains of molecules. In vitro antitumor activities against Tca8113 human tongue cancer cells and L1210 murine leukemia cells were evaluated. A total of 8 of the 12 compounds had higher inhibitory activities than hydroxyurea against L1210 cells. Among them, the most promising compounds were 3e, 3d, 3a and 2d.