Physiological cell death is an essential event in normal development and maintenance of homeostasis. Recently, the morphological and pharmacological characteristics of programmed cell death, which are distinct from those of apoptosis under physiological and pathological conditions, have been reported. However, the molecular mechanism and executioner of this type of cell death are unknown. We show that overexpression of hematopoietically expressed homeoprotein (Hex), a homeoprotein of divergent type, and enhanced green fluorescent protein (EGFP) fusion protein (Hex-EGFP) induces cell death in mouse chondrogenic cell line ATDC5. The expression rate of Hex-EGFP decreased more rapidly than that of EGFP 96 h after transfection. The time-lapse image of living cells revealed the Hex-EGFP-positive cells rapidly died in a necrosis-like fashion. The nuclei of Hex-EGFP-expressing cells were rarely fragmented; however, these cells were negative for terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) staining. The expression rate of Hex-EGFP clearly increased by treatment with radical scavengers, propyl gallate and butylated hydroxyanisole, slightly increased with a caspase inhibitor, zVAD-fmk, and was not affected by N-acetyl cysteine in ATDC5 cells. A fluorescent probe indicated that reactive oxygen species (ROS) were localized near the nuclei in Hex-EGFP-positive cells. In differentiated ATDC5 cells, as hypertrophic chondrocyte-like cells, the expression rate of Hex-EGFP increased above that in uninduced ATDC5 cells. These results suggest that Hex induces nonapoptotic cell death through local accumulation of reactive oxygen species, and mature chondrocytes, which express Hex, might be able to escape cell death induced by Hex in cartilage.