eccDNA, extrachromosomal circular DNA, is a regular component in eukaryotic cells, such as yeast, mouse, pigeon, humans. eccDNA originates from the chromosomes, and it is formed in the cells following DNA damage and repair. Studies suggest that DNA damage accumulates in cells during aging. However, little is known about the dynamic changes of eccDNA in mice during aging, even though mice are the most commonly used disease model. We hypotheses that the quantity and size distribution of eccDNA will change dynamically as cells age and there are some tissue-specific eccDNAs, which affect the function of normal proteins by regulating transcripts in specific tissues. Here, we use mouse samples from four different ages across ten tissues, high-throughput sequencing technology, and bioinformatics methods to study the production and dynamic changes of eccDNA during cell aging in mice.