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l -Canavanine, a natural l -arginine analog, is known to possess cytotoxicity to tumor cells in culture and experimental tumors in vivo. In this study, we first show that apoptotic cell death is associated with antitumor activity of l -canavanine against human acute leukemia Jurkat T cells. When Jurkat T cells were treated with 1.25–5.0 mM l -canavanine for 36 h, apoptotic cell death accompanying several biochemical events such as caspase-3 activation, degradation of poly(ADP-ribose) polymerase (PARP), and apoptotic DNA fragmentation was induced in a dose-dependent manner; however, cytochrome c release from mitochondria was not detected. Under these conditions, the expression of Bcl-2 and its functional homolog Bcl-xL was markedly upregulated. The l -canavanine-induced caspase-3 activation, degradation of PARP, and apoptotic DNA fragmentation were suppressed by ectopic expression of Bcl-2 or Bcl-xL, both of which are known to play roles as anti-apoptotic regulators. These results demonstrate that the cytotoxic effect of l -canavanine on Jurkat T cells is attributable to the induced apoptosis and that l -canavanine-induced apoptosis is mediated by a cytochrome c -independent caspase-3 activation pathway that can be interrupted by Bcl-2 or Bcl-xL.