This work involves synthesis of different five and six member heterocyclic rings starting from phenyl acetic acid. This work is divided into four different parts: First part: This part involved the synthesis of phthalazin-3,8-dione [7] and pyridazin-3,6-dione [6], pyrazole [4,5] and thiadiazole[8] derivative derived from phenyl acetyl hydrazide[3] . as shown in scheme I. Second part: This part involved the synthesis of .oxazole [10]and thiazole[12] derivatives via the reaction of ethyl phenyl acetate with urea and thiourea and cyclization of the resulted products with p-phenyl phenacyl bromide,as shown in cheme II. Third part: This part involved the synthesis of thiosemicarbazide [13], semicarbazide [20], 1,3,4-Oxadiazole [23,18,19], Thiazolidine [16], N-substituted-?4-Oxazoline [22], Oxapyridazine-6-one [17] and 1,2,4-triazole [15,21], 1,3,4-thiadiazole [14] derivatives derived from phenyl acetyl hydrazide [3], 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 and taphylococcus aureus}, as shown in table (4-1).