Objective To explore the impact of peptidylarginine deiminase 2 (PADI2) knockout on depressive-like behaviors in socially isolated mice. Methods Using CRISPR/Cas9 technology, a PADI2 knockout (PADI2-/-) mouse model on a C57BL/6 background was established, and the knockout effect of PADI2 was identified by genotyping and qPCR detection; 6-week-old male PADI2-/- mice and wild-type C57BL/6 mice were selected and divided into normal rearing and social isolation groups, with 15 mice per group, the normal rearing group housed 5 mice per cage, and the social isolation group housed 1 mouse per cage, weighing once a week, after 4 weeks, forced swimming and open field tests were conducted; after the behavioral experiments, brain tissues of mice from each group were taken, and changes in microglia in the mouse brain were detected by immunofluorescence. Results Successfully established PADI2-/- mice, there was no difference in behavior between PADI2-/- mice and C57BL/6 mice in the normal rearing group; after social isolation, compared with C57BL/6 mice, PADI2-/- mice showed a significant increase in depressive symptoms, obvious weight gain, and a significant increase in the number of microglia in brain tissue. Conclusion PADI2 knockout exacerbates depressive-like behaviors and obesity in socially isolated mice, indicating that PADI2 is involved in the progression of depression and may be an effective target for the prevention and treatment of depression.