BackgroundHairfollicle development in Tan sheepdiffers significantly between the birth and Er-mao periods, but the underlying molecular mechanism is still unclear.MethodsWe profiled the skin transcriptomes of Tan sheepinthe birth and Er-mao periods via RNA-seq technology. TheTan sheep examined consisted ofthree sheep inthe birth period and threesheep inthe Er-mao period. ResultsA total of 364 differentially expressed genes (DEGs) in the skin of Tan sheepbetweenthe birth period and the Er-mao period were identified, among which 168 were upregulated and 196 were downregulated. Interestingly, the FOS proto-oncogene(FOS)(fold change=22.67, P value=2.15*10^-44)was the most significantly differentially expressed gene. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis found that the FOS gene was significantly enriched in the signaling pathway related to hair follicle development. Immunohistochemical analysis showed that the FOS gene was expressed in the skin of Chinese Tan sheep at the birth and Er-mao periods,with abnormally high expression in the Er-mao period. Conclusions Our findings suggest that the FOS gene promotes hair follicle development in Tan sheep.