5-(P-Florobenzylidene ) -3-(P-Chlorophenyl )-2-substituted-1,2,4-triazine-6-ones ( 2 and 3 ) were prepared via cyclocondensation of 1,3-oxazolinon derivative (1) with hydrazine hydrate and thiosemicarbazide . Treatment of compound (3) with phenacyl bromide and P-hydroxyl benzalhyde yeilded the corresponding to 5-(pflorobenzylidene)-3-(p-chlorophenyl)-2-(5-phenyl-1,3-thiazol-2-yl) -1,2,4-triazine-6-one (5) and 5-(pfiorobenzylidene) -3-(p-chlorophenyl)-2(p-hydroxy benzylidene amino) thiocarbonyl-1,2,4-triazine-6-one(7). Acetylation of compound ( 2 ,5 and 7) with acetic anydriede led to the formation of monoacetyl and diacetyl derivatives ( 4 ,6 and 8 ) .The structure of synthesized compounds were established with IR ,NMR ,MS and elemental analysis. Some of the new 1,2,4-triazine derivatives were evaluated for cytotoxicity activities.