Chlorine (Cl₂) is an important industrial chemical. Accidental full body exposure to Cl₂ poses an environmental, occupational, and public health hazard characterized mainly by injury to the lung, skin, and ocular epithelia. The cellular mechanisms underlying its acute toxicity are incompletely understood. This study examined whether whole body exposure of BALB/c mice to Cl₂ in environmental chambers leads to the up-regulation of the unfolded protein response (UPR) in their lungs and skin. Shaved BALB/c mice were exposed to a sublethal concentration of Cl₂ (400 ppm for 30 min) and returned to room air for 1 or 6 hours and killed. IL-6 and TNF-α were increased significantly at 1 and 6 hours after Cl₂ exposure in the lungs and at 6 hours in the skin. These changes were accompanied by increased UPR signaling (i.e., activation of protein kinase RNA-like endoplasmic reticulum kinase, inositol-requiring enzyme 1 α, and activating transcription factor 6α) at these time points. The expression of hepcidin, which regulates tissue accumulation and mobilization of iron, was increased in the skin and lungs of Cl₂–exposed mice. The data shown herein indicate for the first time the up-regulation of UPR signaling and hepcidin in the skin and lungs of Cl₂–exposed mice, which persisted when the mice were returned to room air for 6 hours.