<title>Abstract</title>Establishing correct neuronal cell identity is essential to build intricate neural tissue architecture and acquire precise neural function during vertebrate development. While it is known that transcription factors play important roles in retinal cell differentiation, the contribution of epigenetic factors to establishing cell identity during retinal development remains unclear. We previously reported that Samd7, a rod photoreceptor cell-specific sterile alpha motif (SAM) domain protein, functions as a Polycomb repressive complex 1 component (PRC1) that is essential for establishing rod identity. In the current study, we analyzed a functional role of Samd11<italic>,</italic> another photoreceptor-enriched SAM-domain protein<italic>,</italic> in photoreceptor differentiation and maturation. We observed that Samd11 interacts with Phc2 and Samd7, suggesting that Samd11 is a component of PRC1 in photoreceptor cells. We generated <italic>Samd11</italic>-null allele and established <italic>Samd7/11</italic> double knock-out (DKO) mouse. The <italic>Samd7/11</italic> DKO retina exhibits shortened photoreceptor outer segments by electron microscopy analysis. Microarray analysis revealed that <italic>Samd7/11</italic> DKO up-regulated more retinal genes than <italic>Samd7</italic>^{<italic>−/−</italic>} alone, partial functional redundancy of <italic>Samd7</italic> and <italic>Samd11</italic>. Taken together, the current results suggest that Samd7 and Samd11 are PRC1 components and that Samd7 is the major regulator while Samd11 is an accessory factor used for the establishment of precise rod photoreceptor identity.