Some fused heterocyclic oxazoles and imidazols rings were synthesized from reaction of N- acetyl cysteine with different treatment. After thiol group protection, N-acetyl-S-ethyl cysteine (2) had been esterified to give ester 3 which cyclized to oxazole 4 with phosphorus oxychloride. N-acetyl-S-ethyl cysteine 2 were converted to acid chloride 5 with thionyle chloride. Amide 6 were synthesized from 5 with ammonia solution. Amide 6 converted to substituted carbamide 7 by react with P2S5, then the product reacted with α-chloroacetophenone to give substituted thiazol ring 8 that converted to bicyclic thiazole – imidazole ring system 9. Cyclized benzoxazole derivative 10 had been synthesized then converted to 3-(ethylthio)-1-methyl-1,3a-dihydrobenzo[d]imidazo[5,1-b]oxazole (11). Structure of new synthesized compounds were confirms by IR ,1H-NMR, and UV spectra as well as physical constant.