Several acyclonucleoside analogues of pyrimidine base and N$^1$-derivatives of 5-fluorouracil have been synthesized and evaluated for their biological effects. When tested with in vitro Lekemia L1210 cells, the 5-fluorouracil derivatives exhibited slightly higher antitumor activity than the parent 5-fluorouracil. When tested against Herpes Simplex Virus type 1 and type 2 cultured in the Vero cell, the 5-fluorouracil derivatives showed weak antiviral activity.