Competitive environments promote high testosterone levels, oxidative stress and, consequently, impair cellular homeostasis. The regulation of genes involved in the synthesis of the pigment pheomelanin in melanocytes seems to help to maintain homeostasis against environmental oxidative stress. Here, social interactions in some zebra finch Taeniopygia guttata males were experimentally increased by keeping them in groups of six birds during feather growth, while others were kept alone, to test if melanocytes show epigenetic lability under a competitive social environment. As these changes may depend on the oxidative status, buthionine sulfoximine (BSO) was administrated to decrease the antioxidant capacity of some birds. The competitive environment downregulated a gene involved in pheomelanin synthesis (Slc7a11) by changing the level of DNA methylation in feather melanocytes. In other genes involved in pheomelanin synthesis (Slc45a2, MC1R and AGRP), DNA methylation was also affected, but no changes in expression were detected. The exposure to the competitive environment did not affect systemic oxidative stress and damage, indicating that a protective epigenetic mechanism that changes the expression of Slc7a11 may have been activated. However, no changes on the pigmentation phenotype of birds were found, likely due to the short duration or low intensity of the competitive environment. BSO treatment did not affect the epigenetic mechanism, suggesting that the antioxidant capacity of birds was high enough to deal with the competitive environment. An epigenetic mechanism limiting pheomelanin synthesis gets therefore activated under exposure to a competitive environment in male zebra finches, which may help avoiding damage caused by competitive interactions. informacion[at]ebd.csic.es: Rodríguez-Martínez & Galván (2019) Exposure to a competitive social environment activates an epigenetic mechanism that limits pheomelanin synthesis in zebra finches. Molecular Ecol https://doi.org/10.1111/mec.15171