The immediate early response gene X-1 (IEX-1) is involved in regulation of various cellular processes including proliferation, apoptosis in part by controlling homeostasis of reactive oxygen species (ROS) at mitochondria. The present study shows reduced inflammatory responses and colorectal cancer in IEX-1 knockout (KO) mice treated with azoxymethane/dextran sulfate sodium (DSS). However, DSS induced worse colitis in RAG^−/−IEX-1^−/− double KO mice than in RAG and IEX-1 single KO mice, underscoring an importance of T cells in IEX-1 deficiency-induced protection against colon inflammation. Lack of IEX-1 promoted the differentiation of interleukin (IL)-17–producing T cells, concomitant with upregulation of Gαi2 expression, a gene that is well-documented for its role in the control of inflammation in the colon. In accordance with this, T-helper 17 (T_H17) cell differentiation was compromised in the absence of Gαi2, and deletion of Gαi2 in T cells alone aggravated colon inflammation and colorectal cancer development after azoxymethane/DSS treatment. Null mutation of IEX-1 also enhanced both proliferation and apoptosis of intestinal epithelial cells (IEC) after injury. A potential impact of this altered IEC turnover on colon inflammation and cancer development is discussed. These observations provide a linkage of IEX-1 and Gαi2 expression in the regulation of T_H17 cell differentiation and suggest a previously unappreciated role for IEX-1 in the control of colon epithelial homeostasis. Mol Cancer Res; 10(6); 760–7. ©2012 AACR.