Chemical transformation of 3-amino-5-hydroxy-4-phenylazo-1H-pyrazole (1) provided a series of new pyrazol derivatives such as N-(4-(2-phenyldiazenyl)-2,5-dihydro-3-hydroxy-1H-pyrazol-5-yl)-2 chloroacetamide (2) obtained in the reaction of 1 with chloroacetyl chloride. Reaction of 2 with malononitrile and ammonium isothiocyanate gave the corresponding 1-(4-(2-phenyldiazenyl)-5-hydroxy-1H-pyrazol-3-yl)-2-amino-4,5-dihydro-5-oxo-1H-pyrrol-3-carbonitrile (3) and 3-(2-phenyldiazenyl)-7-amino-2-hydroxypyrazolo[1,5-a]pyrimidin-5(1H)-one (4). Reaction of 1 with P2S5 gave the corresponding 3-amino-5-mercapto-4-phenylazo-1H-pyrazole 5. The reaction of compound 5 with chloroacetic acid, ethyl chloroacetate, tetrahydrofuran, 3-hydroxybenzaldehyde, phenacylbromide and ninhydrine gave the corresponding N-substituted derivatives (6, 7, 8, 9, 10, 11, 12, 13), respectively. The reaction of compound 7 with hydrazine hydrate and a consecutive cyclization in the presence of glacial acetic acid and sulfuric acid mixture afforded 12. 1-(4-(2-Phenyldiazenyl)-5-mercapto-1H-pyrazol-3-yl)-3- phenylthiourea 14 was obtained from reaction of 5 with phenyl isothiocyanate, which was transformed into pyrazolothiadiazole 15 and pyrazolotriazole 16 derivatives with bromine in different solvents. 3-Amino-5-hydrazino-4-phenylazo-1H-pyrazole 17 was obtained from reaction 5 with hydrazine hydrate. Cyclization of compound 17 by reacting it with ethyl acetoacetate, acetylacetone, phthalic anhydride and phenacyl bromide gave the corresponding N-pyrazolylpyrazoles (18 and 19), pyrazol-2,3-dihydrophthalazine-1,4-dione (20) and pyrazolotriazine (21), respectively. Reaction of 17 with sodium nitrite in the presence acetic acid, ethyl pyruvate and carbon disulfide gave the corresponding pyrazolotetrazole (22), imidazolopyrazole (23) and pyrazolotriazole derivatives (26).