During embryonic development, a single totipotent cell, the egg, gives rise to all embryonic and extra-embryonic tissues. After the first differentiation steps, pluripotent cells have the capacity to generate all somatic lineages and the germline and can be maintained indefinitely in vitro. In mice, they can be derived from the Inner Cell Mass (ICM) of blastocysts (Embryonic Stem cells, ESCs) or later from epiblast (Epiblast Stem cells, EpiSCs) of egg cylinders. Somatic cells can be converted into induced pluripotent cells (iPSCs) by over-expressing 3 or 4 specific exogenous factors. ESCs, iPSCs and EpiSCs share the ability to differentiate in vitro into the three germ layers. However, only ESCs and iPSCs can contribute to fetal development after injection into pre-implantation embryos, whereas EpiSCs cannot. These two distinct states of pluripotency are designated as naïve (ESCs/iPSCs) and primed (EpiSCs) states. mESCs initially cultured in media containing serum and Leukemia inhibitory factor (LIF) have been shown to be heterogeneous with fluctuating pluripotency states. However, when cultured in serum free medium in the presence of two inhibitors (2i) targeting MEK1/2 and GSK3α/β pathways, the cells reach a homogeneous state called naïve ground state. Endogenous retrovirus (ERVs) are marks of ancient retroviral integrations into genomes. Some ERVs are transcribed during early embryo development in mouse, chicken, bovine and human, and their expression patterns fluctuate during early development. We exploited these ERV reactivation properties to express fluorescent reporters according to the pluripotency status of targeted cells. Introduced into mESCs, these reporters have highly specific expression profiles depending on cell culture conditions. Consequently, we demonstrated that the reversion of mESCs into the naïve ground state by transitioning from a serum/LIF condition to a 2iLIF condition takes several cell divisions and passes through several transient states. Thanks to the activities of those ERV reporters, we were able to enrich populations with different transcriptional profiles, demonstrating varying different abilities to participate in embryonic development when injected into mouse embryo. These ERVs derived reporters hold considerable potential for identifying and subsequently isolating cells based on their different pluripotency status, enabling us to decipher the different phases of cell reversion into naïve ground state. Altogether, those reporters could efficiently help isolate PSCs from the embryos with the desired pluripotency state.