Abstract: Objective To investigate molecular mechanism of apoptosis induced by diallyl disulfi de (DADS) in human glioblastoma U251 cells. Methods Morphological analysis, MTT, fl ow cytometry, Western blot and immunocytochemical technique were used to observe the effects of apoptosis and its expression of related proteins in human glioblastoma U251 cells induced by DADS. Results After exposure to DADS, partial U251 cells presented characteristic morphological changes of apoptosis under the light microscopy. MTT assay showed that 15, 30, 45, 60 mg/L DADS signifi cantly inhibited proliferation of U251 cells at 48 h, its inhibition ratio were 22.01%, 38.82%, 49.23% and 55.27%, respectively, in dose-dependent manner (P<0.05). Flow cytometry analysis showed that U251 cells treated with 15, 30 and 45 mg/L DADS for 48h signifi cantly increased the percentage of apoptosis cells, its apoptosis rate were(5.36±0.87)%, (28.36±3.15)% and (44.58±3.95)%, respectively, higher than (2.14±0.45)% of untreated cells (P<0.05). Immuocytochemistry detect revealed that expression of Bcl-2 decreased from 0.75±0.06 to 0.34±0.03, and Bax and Caspase 3 expression increased from 0.26±0.03 and 0.19±0.02 to 0.63±0.04 and 0.41±0.05, respectively, in average optical value (P<0.01). Western blot showed that downregulation of Bcl-2 expression was 1.21±0.18, 0.89±0.14 and 0.41±0.09 lower than 2.24±0.26 of untreated cells, and upregulation of Bax and Caspase 3 was 1.12±0.19, 1.54±0.22 and 2.08±0.27 and 0.72±0.15, 1.39±0.21 and 2.28±0.29, higher than 0.33±0.08 and 0.14±0.06 of untreated cells, respectively, in gray scale value after U251cells treated by 15, 30 and 45 mg/LDADS (P<0.05). Conclusion DADS can induce apoptosis of U251 cells related to downregulation of Bcl-2 expression and upregulation of Bax and Caspase 3.