Some novel substituted pyrazoles 4a-t were synthesized from hydrazone synthons 3a-x after reaction with hydrazine hydrate. The hydrazones 3a-x were afforded through coupling of their corresponding diazonium salts with ethyl cyanoacetate, malononitrile, acetyl acetone and ethyl acetoacetate, respectively. The antiviral activity of such compounds was evaluated against a wide set of viruses; adenovirus type 7, rotavirus, HSV-1 and HCV viruses in different cell lines. Amongst the tested compounds, 3b, 3h, 3p, 3w, 4g, 4q and 4r showed significant antiviral activity. Compounds 4g and 4r particularly exhibited the highest activity of all the tested title compounds against all the study viruses. On the other hand, compounds 3b, 3h, 3p, 4g, 4q and 4r showed significant anti-HSV-1 activity. Hydrazones 3b and 3h showed moderate anti-HCV activity. Pyrazoles 4q and 4r showed moderate activity against adenovirus type-7. On the contrary, the title pyrazoles 4a-t showed no significant anti-HCV activity and the title hydrazones 3a-x had no significant antiviral activity against adenovirus type-7.