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A number of N-acyl and N-(alkoxycarbonyl)-5-fluorouracil derivatives possessing, for example, benzoyl, o-toluyl, acetyl, propionyl, heptanoyl, ethoxycarbonyl, phenoxycarbonyl, and benzyloxycarbonyl groups as N1 and/or N3 substituents were synthesized, and their antitumor activities were evaluated. The synthesis was achieved by a direct and two-step acylation of 5-fluorouracil and by selective N1-deacetylation of N1-acetyl-N3-substituted-5-fluorouracil under appropriate reaction conditions. Several N3-benzoyl- and N3-o-toluyl-5-fluorouracil derivates and showed significant activity against experimental tumor, and N1-acetyl-N3-o-toluyl-5-fluorouracil was found to be most promising among them. Further investigation revealed 12 to retain higher activity toward various tumors, with lower toxicity and good blood level, than either 1 or FT-207, even for oral administration.