Pyrimidine carbocyclic nucleosides with a hydroxyamino group instead of a hydroxymethyl group at the 4'-position of the sugar moiety were designed as potential antitumor and/or antiviral agents. Pd (O)-catalyzed reactions of enantiomerically pure (+)-(1R,4S)-4-[(tert-butyldiphenylsilyl)oxy]-1-(ethoxycarbonylo xy)-2- cyclopentene (9) with N3-benzoylthymine and -uracil gave carbocyclic nucleosides 10 and 11. Subsequent Pd (O)-catalyzed reactions of N3-benzoyl-1-[(1R,4S)-4-(ethoxycarbonyloxy)-2-cyclopenten-1- yl]thymine (14) and -uracil (15) with O-benzylhydroxylamine smoothly gave the hydroxyamino-substituted carbocyclic nucleosides 16 and 17. From these nucleosides, the target compounds were prepared after deprotection or further reactions. The 2',3'-didehydro-2',3'-dideoxythymidine (D4T) analogue 20 was the most effective compound, with IC50 values of 27.3 and 34.5 microM against KB and L1210 cells in vitro. Carbocyclic analogues of uridine and cytidine (29 and 32) were less effective than 20 against both cell lines.