UVB irradiation is a major pathological factor that disrupts skin tissue homeostasis by inducing apoptosis, oxidative DNA damage, and alteration of the dermal extracellular matrix (ECM). This study evaluated the multifaceted effects of carboxymethyl chitosan (CMC), a water-soluble chitosan derivative modified with carboxymethyl functional groups, on ECM remodeling, anti-inflammatory activity, and antimicrobial activity in a UVB-induced skin pathology model. CMC significantly increased type I and III collagen expression in human dermal fibroblasts by activating the TGF-β1/CTGF signaling pathway. Based on this cellular-level remodeling activity, an in vivo subcutaneous injection model using normal mice showed that CMC promoted recruitment of mesenchymal stem cells (CD29⁺/CD90⁺; MSCs) into the dermal layer. Furthermore, CMC application in a UVB-induced skin pathology model induced expression of matrix proteins, including collagen and elastin, in the damaged dermis, resulting in significant recovery of ECM physiological balance. In addition, CMC effectively attenuated inflammatory responses associated with UVB-induced apoptosis and oxidative DNA damage and exhibited potent inhibitory activity against major skin pathogens. In conclusion, CMC is a promising bioactive material capable of promoting tissue homeostasis recovery in a UVB-induced skin pathology model through recruitment of MSCs, promotion of ECM remodeling, and anti-inflammatory and antimicrobial activities.