There are experimental evidences that chronic social defeat stress is accompanied by development of anxiety- and depression-like state as well as downregulation of serotonergic genes in the midbrain raphe nuclei of male mice. The study was aimed at investigating the effect of chronic lithium chloride (LiCl) administrations on anxiety behavior and the expression of serotonergic genes in the midbrain raphe nuclei of affected mice. The pronounced anxiety in male mice was caused by chronic social defeat stress in daily agonistic interactions. After 6 days of social stress, defeated mice were treated with saline or LiCl (100 mg/kg, i.p. two weeks) against the background of continuing agonistic interactions. The level of anxiety was assessed using behavioral tests. The effect of chronic treatment with LiCl on the expression of serotonergic genes in the midbrain rapher nuclei was also studied. Mild anxiolytic effects of LiCl were found on communication in the partition test. Anxiogenic-like effects assessed using the elevated plus-maze and social interaction tests were found. Chronic LiCl treatment induced overexpression of the serotonergic genes in the midbrain raphe nuclei. The effects of chronic LiCl treatment depends on the method of treatment, psychoemotional state, and experimental context (tests).