The 1H-pyrazole-3-carboxylic acid 2 and its remarkably stable acid chlorides 3 can easily be converted into the corresponding carbohydrazide, ester or amide derivatives 4, 6 and 7, respectively, from reaction with alcohols or N-nucleophiles. The acid chloride (3) was also converted easily into the new derivatives consisting of 5-phenyl-1H-pyrazole 8a,b. The cyclocondensation reactions of 2 with some hydrazines led to the formation of pyrazolo[3,4-d]pyradizinone 5 derivative. The nitrile derivative 9 was obtained by dehydration of 7a, b in a mixture of SOCl2 and DMF. The thermal decomposition of 4-Benzoyl-1-(4-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid 2b leads to the formation of [1-(4-nitrophenyl)-5-phenyl-1H-pyrazole-4-yl] phenylmethanone 10) It has been demonstrated that with the variation in reaction conditions, the reaction changes and leads to different products. The structures of these newly synthesized compounds were determined from the FT-IR, H-1 and C-13 NMR spectroscopic data and elemental analyses.