In olfactory pathway of mammals, the olfactory recepors in the olfactory mucosa give rise to the olfactory nerve, which terminate in the olfactory bulb. The layers and neurons of the olfactory bulb from surface inward are olfactory nerves, olfactory glomeruli, external plexiform layer, mitral cell body layer, internal plexiform layer and granule cell body layer. The olfactory axons all terminate in olfactory glomeruli, which are regions of neuropil, composed on the one hand of the terminals of the olfactory nerve axons and on the other of the dendritic tufts of three types of bulbar neurons ; mitral, tufted, and periglomerular cells. This study was performed to identify ultrastructural changes of the synapses in the olfactory glomeruli of the rat after nasal irrigation with 1% aqueous solution of zink sulfate(ZnSO₄, a compound known to selectively damage olfactory epithelium). Under the electron microscopic examination, we found the following results ; 1) During the first 3 days, we detected swelling of synaptic vesicles, mitochondrial pyknosis, more darkening of axoplasm in the densely stained terminals and all of which formed of asymmetrical axo-dendritic synapses. 2) During the 5 days to 56 days after treatment, we observed indistinct appearance of synaptic vesicles, vacuolization of axoplasm and atrophy of entire axon terminal in the same terminals. 3) During the experimental period, the areas of the processes of the neuroglial cells were increased gradually in neuropil of the olfactory glomeruli. It concluded that terminals of olfactory nerve filled with round synaptic vesicles of variable size in diameter and had a densely stained axoplasm and made of asymmetrical axo-dendritic synapses in olfactory glomeruli. It is suggested that destruction of the olfactory epithelium with 1% zink sulfate solution cause decrease of the entire volumn of olfactory bulb and occur anosmia.