Abstract： Objective To investigate the effect of phenylhexyle isothiocyanate (PHI) on demethylation and activation of transcription gene p15 in acute leukemia cell line Molt-4. Methods DNA sequencing and modified methylation specific PCR (MSP) were used to screen p15-M and p15-U mRNA after Moh-4 cells were treated with PHI. P15 mRNA was measured by RT-PCR. Pl5 protein was detected by Western blotting. Results Hypermethylation of gene pl5 was apparently attenuated and activation of transcription p15 gene was de novo after 5 days exposure to PHI. PHI enhanced both the expression of p15 mRNA and p15 protein in a concentration-dependent manner. The ratio of the gray scale of p15 mRNA strap was 0.17±0.12 in control, 0.29±0.14 in PHI 10 μmol/L, 0.55±0.07 in PHI 20 μmol/L, 0.93±0.13 in PHI 40 μmol/L. Conclusion PHI could active demethylation and transcription of gene p15.