In the present research work a new series of 1,3,4-oxadiazole & pyrazolone derivatives have been synthesized. 2-mercapto-1,3,4-oxadiazole derivatives were synthesized by reacting corresponding acid hydrazide with carbon disulfide followed by condensing the active hydrogen atom of 2-mercapto group of 5-aryl-2-mercapto-1,3,4-oxadiazole with 2-chloro pyridine, 4-chloro aniline & epichlorohydrine to give 5-aryl-2-(substituted aryl ylthio)-1,3,4-oxadiazole derivatives(A1-3, B1-4). 5-(substituted aryl)-1,3,4-oxadiazole derivatives were synthesized by reacting salicylic acid hydrazide with aromatic acid to give 5-(2-hydroxy phenyl)-2-aryl-1,3,4-oxadiazole derivatives (A4-6): 3-methyl-pyrazol-5(4H)-one derivatives were synthesized by reacting corresponding acid hydrazide with ethyl acetoacetate to give 1-(substituted aryl)-3-methyl-1H-pyrazol-5(4H)-one. Followed by condensing the active hydrogen atom of ¿CH2- of pyrazolone with Isonicotinic acid hydrazine/ p-amino salicylic acid/ sulfanilamide / 5-amino tetrazole / pyrazinoic acid hydrazide / 2-amino pyrazine to give corresponding pyrazolone derivatives (A7-11, B5-9).