Selenoprotein S is one of the newly identified mammalian selenoproteins and is suggested to play a role in the endoplasmic reticulum associated protein degradation (ERAD) pathway; however, its function and expression during embryonic and fetal development are still unknown. This study investigated the pattern of expression of SelS as well as Derlin1, and P97ATPase during embryonic and fetal development in rats. Whole embryos of age 6.5 to 11.5 day post copulation (dpc) as well as embryonic and fetal liver, brain, lungs, kidneys, and intestine were collected between 15.5 and 19.5 dpc. The expression ofSelS, derlin1, and P97ATPasewas determined by RT-PCR assays SelS , Derlin1 and P97ATPase were found to be constitutively expressed in rat whole embryos at least at 6.5 dpc and embryonic and fetal tissues between 15.5 and 19.5 dpc. There was a peak of increase in the expression of SelS at 13.5 dpc in rat whole embryos. The highest expression of SelS was detected in the lungs. SelS shared some common expression patterns with Derlin1 and P97ATPase where they showed high expression in whole embryos between 6.5 and 13.5 dpc. The three genes showed an increase in the expression in the brain between 15.5 and 17.5 dpc and a decreased expression in the liver, heart, and the intestine in newborns at age of 2 days. In addition the three genes showed an increase in the expression in the heart between 19.5 dpc and newborns at age of 1 day. Therefore, the constitutive expression of SelSduring all stages of embryonic and fetal development at least from 6.5 dpc is vital and maybe involved with Derlin1 and P97ATPase in the initiation or ERAD pathway to prevent the occurrence of ER-Stress mediated apoptosis.