Reaction of 3-amino-5-hydroxy-4-phenylazo-1H-pyrazole (1) with phenacyl bromide, acetic acid anhydride, benzoyl chloride and aromatic aldehydes gave 3-N-alkylated/acylated derivatives (2, 4 and 5) and the corresponding Schiff bases (6), respectively. Ring closure for compound 2 in acetic anhydride afforded pyrazolopyrimidine 3. Reaction of 1 with acetylacetone, ethyl acetoacetate, ethyl cyanoacetate, diethyl malonate and ninhydrine resulted in pyrazolo[1,5-a]pyrimidine-5(H)-one (7, 8, 9), pyrazolo[1,5-a]pyrimidine-5,7(1H,6H))-dione (10) and pyrazol-3-ylimino-1H-indene-1,3-(2H)-dione (12) derivatives. Reaction of active methylene group of (phenyldiazenyl)pyrazolo[1,5-a]pyrimidin-5,7(1H,6H)-dione (10) with phenyldiazonium chloride gave 2-phenylhydrazono derivative (11). Moreover, reaction of 1 with POCl3 and P2S5 resulted in 5-chloro (13) and 5-mercapto (15) derivatives, while phthalic anhydride, chloroacetyl chloride, aroyl thiocyanates and ammonium thiocyanate gave the corresponding 3-N-substituted derivatives. Hydrazenolysis of 13 in presence of hydrazine hydrate afforded the 5-hydrazino derivative. The 2-mercapto -7-(phenyladiazenyl)-2,5-dihydropyrazolo[1,5-b]triazole-6-ol (20) and 2-amino -7-(phenyladiazenyl)-2,5-dihydropyrazolo[1,5-b][1,2,4]-thiadiazol-6-ol (21) were obtained by the reaction of 1-(5-hydroxy)-4-(phenyldiazenyl)-1H-pyrtazol-3-yl)thiourea with bromine in different solvents. The structures of newly synthesized compounds have been established by IR, 1H NMR and elemental analysis.