GVHD (Graft-versus-Host Disease) results from the cytotoxic T lymphocytes from the bone marrow recognizing the recipient's minor histocompatibility antigens. In experimental murine models, either CD4+ or CD8+ T-cell subsets can cause GVHD, depending upon the particular strain combination utilized. Recent studies suggest that the keratinocyte undergo apoptosis in GVHD. However, morphological data supporting this concept are still lacking. The present study was undertaken in order to document apoptosis in experimental acute GVHD via sequential analysis of ultrastructure .Acute GVHD was produced across minor histocompatibility loci using appropriately matched murine strains. Acute GVHD was mediated with the use of highly purified preparations of donor CD4+ and CD8+ T-cell subsets. Whole T cells were used as a positive control and T cell depleted bone marrow as a negative control. Conventional transmission electron microscopy was used to define apoptosis structurally Sequential ultrastructure revealed that the keratinocyte underwent apoptosis in CD4+, CD8+ and whole T cell groups. This study demonstrates the sequential ultrastructure of the keratinocyte undergoing apoptosis from the beginning to the end. Both of the basal and the suprabasal keratinocytes show the morphology of early apoptosis, and the detachment of the tonofibril from the basement membrane and the adjacent cell was the general findings in the apoptotic cell Sequences of the cytoplasmic condensation was demonstrated . Through ultrastructural quantitation the apoptotic indices were depicted in all the experimental groups. Characteristically, numerous lymphocytes underwent apoptosis in CD8+ groups at day 28 and 35.