Abstract: Four 5-(p-substituted-phenylazo)-uracils (Ⅴ:Ⅴa,Ⅴb,Ⅴc and Ⅴd)and six 5-(p- substituted-phenylazo)-6-methyluracils (Ⅵ:Ⅵa,Ⅵb,Ⅵc,Ⅵd,Ⅵe and Ⅵf)were pre- pared as antitumor agents,However,none of them showed any significant activity against Ehrlich ascites tumour in mice. (Ⅴa)R=C1 mp.280°dec.(Ⅵa)R=G1 mp.235°dec. (Ⅴb)R=Br mp.270°dec.(Ⅵb)R=Br mp.227°dec. (Ⅴc)R=CH₃ mp.264°dec.(Ⅵc)R=CH₃ mp.223°dec. (Ⅴd)R=SCN mp.171°dec.(Ⅵd)R=OCH₃ mp.235°dec. (Ⅵe)R=SCN mp.147°dec. (Ⅵf)R=SCH₃ mp.222°dec. A of 5-substituted uracils and methyluracils (Ⅶ:Ⅶa,Ⅶb,Ⅶc,Ⅶd and Ⅷ: Ⅷa,Ⅷb,Ⅷc,Ⅷd,Ⅷe,Ⅷf,Ⅷg,Ⅷh)were also prepared.These uracils did not show any significant inhibiting action against Sarcoma 180 in mice.The phar- macological actions of the above compounds will be reported eleswhere. ^*(Ⅶa)R=NO₂ ^*(Ⅷa)R=NO₂ ^*(Ⅶb)R=NHCHO mp.312°dec.(Ⅷb)R=NHCHO mp.290°dec.^*(Ⅶc)R=NHCOCH₂Cl mp.274°dec.(Ⅷc)R=NHCOCH₂Cl mp.252°dec. (Ⅶd)R=NHCSNH₂ mp.>320°(Ⅷd)R=NHCOCHCl₂ mp.280°dec. (Ⅷe)R=NHCOCH₂I mp.236°dec. (Ⅷf)R=NHCOCF₃ mp.282°dec. (Ⅷg)R=NHCOOC₂H₅ mp.265°dec. (Ⅷh)R=NHCSNH₂ mp.268°dec.