4-Methylsulfinyl-3-butenyl isothiocyanate (MTBITC) found in the radish (Raphanus sativus L.), is a wellknownanticancer agent. In this study, the mechanisms of the MTBITC induction of cell apoptosis in humanA549 lung cancer cells were investigated. Our PI staining results showed that MTBITC treatment significantlyincreased the apoptotic sub-G1 fraction in a dose-dependent manner. The mechanism of apoptosis induced byMTBITC was investigated by testing the change of mitochondrial membrane potential (ΔΨm), the expressionof mRNAs of apoptosis-related genes by RT-PCR, and the activities of caspase-3 and -9 by caspase colorimetricassay. MTBITC treatment decreased mitochondrial membrane potential by down-regulating the rate of Bcl-2/Bax and Bcl-xL/Bax, and activation of caspase-3 and -9. Therefore, mitochondrial pathway and Bcl-2 gene familycould be involved in the mechanisms of A549 cell apoptosis induced by MTBITC.