This work involves synthesis of different five and six member heterocyclic rings starting from acid hydrazides (m-methyl benzoyl hydrazide and p-nitro benzoyl hydrazide) which were synthesized from their carboxylic acids. This work is divided into four different parts: First part: This part involved the synthesis of phthalazin-3,8-dione [8a,8b] and pyridazin-3,6-dione [7a,7b], pyrazole [6a,6b] and 1,3,4-oxadiazole [4a,4b,5b] derivatives from acid hydrazides [3a, 3b], as shown in scheme I. Second part: This part involved the synthesis of 1,2,4-triazole [10a] and Schiff bases [11a] derivatives derived from m-methyl benzoyl hydrazide [3a], as shown in scheme II. Third part: This part involved the synthesis of thiosemicarbazide [12b], semicarbazide [18b], 1,2,4-Triazole [14b,20b], 1,3,4-Oxadiazole [19b], 1,3,4-thiadiazole [13b], Thiazolidine [15b], Pyrazole [17b], N-substituted-?4-Oxazoline [21b] and Oxapyridazine-6-one [16b] derivatives from p-nitro benzoyl hydrazide [3b], as shown in scheme III. Fourth part: This part deals with the study of antibacterial activities of some of the synthesized compounds. These activities were determined in vitro using disc diffusion method against four pathogenic strains of bacteria {Pseudomonas aeuroginosa, Klebsiella pneumoniae, Staphylococcus aureus and Bacillus subtilus}, as shown in table (4-1).