In order to find out a proper connecting bridge between 5-fluorouracil(5-FU) and a macromolecule such as a polypeptide, potentially hydrolytic N$^{1}$-derivartives of 5-FU have been systhesized and evaluated for their biological activity. When tested with in vitro leukemic L$_{1210}$ cells all the obtained derivartives exhibited slightly higher antitumor activity than the parent 5FU. Among them the N$^{1}$ -carbamoyl analogue 2 and N$^{1}$-acetamido analogue 6b showed 50% inhibition of the L$_{1210}$ cell growth at the concentrations of 5.01$ imes$10$^{-8}$M and 1.03$ imes$10$^{-7}$M, respectively. When tested against sarcoma 180 tumor cells inoculated into mice, the compounds 2 and 6b exhibited, respectively, 62% and 54% inhibition of the solid tumor growth at the 5-time doses of 100 mg/kg/day. Both compounds, N$^{1}$-carbamoyl analogue 2 and N$^{1}$-acetamido analogue 6b, realeased the parent 5-FU when incubated in the L$_{1210}$ cell cultural media for 5 hrs.