2,3-Dichloro-1-propanol (2,3-DCP) is a member of a group of chemicals known as chloropropanols. Currently, immunotoxicity of 2,3-DCP has not been reported. In the present study, we studied its inhibitory effects on T cell both in vivo and in vitro. The results showed that 2,3-DCP markedly inhibited ConA-induced splenocyte proliferation, Th1 and Th2 cytokine production, CD4(+) T cell populations, and the ratio of CD4(+)/CD8(+) T cells and cell cycle arrest in vitro. In addition, 2,3-DCP markedly suppressed DNFB-induced T-cell-mediated delayed-type hypersensitivity (DTH) reaction in mice. Furthermore, Western blot was used to study how 2,3-DCP affects signal transduction mechanisms. The data revealed that 2,3-DCP could down regulate activation of ConA-induced NF-κB and NFAT signal transduction pathways. These observations indicated that 2,3-DCP exhibited negative regulatory effects by directly suppressing T-cell-mediated immune responses in vitro and in vivo.