Mucosal surfaces of the trachea and larynx are protected by several complex defense mechanism, namely mucociliary clearance, immune reaction, local reaction by antibacterial secretory products such as lysozyme, lactoferrin, which have also been demonstrated in the mucosa of nasal cavity, middle ear and eustachian tube mucosa. The morphology of secretory glands and cells of the trachea and larynx is well-known, but knowledge concerning their development related to secretory activity is still sketchy. The secretory element of the murine trachea and larynx, aging from gestational day 14 to postnatal day 21, was studied using hematoxylin & eosin and alcian blue/periodic acid-Schiff staining to investigate its development to provide the basis of morphological study of the developing trachea and larynx. The results are as follows ; 1) epithelial secretory cells were stained with AB-PAS at gestational day 18 and the submucous glands were stained at postnatal day 1, although they started to develop during the fetal stage. 2) PAS-positive cells were predominant at postnatal day 1, while both AB- and PAS-positive cells had become numerous since postnatal day 5. 3) The submucous glands were most common at posterolateral part of the subglottis, especially at the junction of trachea. The results of this study suggest that the secretory activity starts to be established immediately after birth with the aeration of the lung.