Purpose: To examine the developmental expression of mucin-like glycoprotein associated with photoreceptor cells (MLGAPC), and to confirm that MLGAPC with a relative mass of 120 and 135 kD correspond to the cone and rod types, respectively. Methods: We isolated the cDNA of the core protein of rat MLGAPC, prepared an anti-rat MLGAPC core protein antibody and then examined the expression of the MLGAPC core protein in postnatal developing rat retinas by means of Western blotting and immunohistochemistry. Results: On postnatal early days when cone photoreceptor cells were thought to be developing, MLGAPC was detected as a single band of 120 kD and was found to be positive in the apical portion of the neuroblastic layer. After postnatal day 7, when rod photoreceptor cells were developing, MLGAPC was detected as a minor band of 120 kD and an additional major band of 135 kD and was present throughout the differentiated photoreceptor and outer plexiform layers. Conclusions: The present findings revealed the developmental expression of MLGAPC and confirmed that MLGAPC of 120 and of 135 kD correspond to the cone and rod types, respectively. This demonstration is advantageous for studying the physiological roles of MLGAPC in the photoreceptor and outer plexiform layers, since the cone- and rod-associated glycoproteins should be investigated separately.