Four new polyesters containing 5-fluorouracil in the main chain were prepared by reacting potassium salt of 5-fluorouracil with ω-chloroalkyl chloroacetates. The chemical structures of these new polyesters had been confirmed by 1H-NMR

IR and elemental analysis. The antitumor activity of one of these 5-fluorouracil containing polyesters

Ⅱ-4 was tested against sarcoma 180

HSC in mice. It showed good antitumor activity and low toxicity. Blood concentration measurements of PFUE-Ⅱ-4 after oral administration to rabbits demonstrated that 5-fluorouracil containing polyester has a longer duration of action than that of low molecular weight drug FT-207.