Objective  To investigate the alteration of mood and hippocampal microglia morphology in a mouse model of chronic inflammatory pain induced by complete Freund’s adjuvant (CFA).    Methods  Thirty-two male ICR mice were randomly divided into two groups, including normal saline control group (NS) and CFA model group (CFA). The pain model was established by right hindpaw intraplantar CFA injection. The change of mechanical pain threshold after CFA injection was measured by von Frey fiber needle, the locomotor activity and anxiety-like behavior were determined by open field test (OFT), the depression-like behavior was determined by sucrose preference test (SPT) and forced swimming test (FST). The expression of microglia marker ionized calcium binding adaptor molecule-1 (IBA-1) in the hippocampus was determined by immunohistochemistry and its morphological change was analyzed by Sholl analysis.   Results  Compared with the NS group, the mechanical pain threshold of CFA group decreased significantly (P<0.01). The behavior result  showed that the CFA group showed remarkably reduced time in the inner area (P<0.01) compared with the NS group in the open field test；In the sucrose preference test, the percentage of sucrose preference (P<0.01) of CFA mice decreased significantly compared with the NS mice, while the immobility time of CFA mice (P<0.01) increased significantly in the forced swimming test compared with the NS mice. The immunohistochemistry showed that the number of microglia in the dentate gyrus (DG) of CFA mice increased significantly compared with the NS mice. The Sholl analysis result  showed that compared with the NS mice, the number of intersections of microglia in hippocampal DG decreased significantly in CFA mice.   Conclusion  Our finding  indicates that the negative emotions in CFA-induced chronic inflammatory pain may be related to the morphological changes of hippocampal microglia in the mice.