Objective To observe the PML protein expression of hepatocellar carcinoma tissue and cells lines and As 2 O3 regulate its expression .Methods Immunohistochemistry was used to examine the PML protein expression of hepatocellar carcinoma tissue . Western blot analysis were used to observe PML protein expression of hepatocellar carcinoma tissue of 12 cases ,5 hepatocellar car-cinoma cell lines ,such as HuH7 ,HepG2 ,Hep3B ,SMMC-7721 ,MHC97H .Western blot analysis was used to detected the PML pro-tein expression of these hepatocellar carcinoma cell lines after 72-96 h treated with 0 .25 μg/mL of As2 O3 .Results Immunohisch-enmical staining showed that the PML protein was expressed in both cytoplasm and nucleus ,did not well-distributed in hepatocellar carcinoma cells .There was no significant differences of PML protein expressed among differently differentiated stages of hepatocel-lar carcinoma cells .Western blot analysis found that hepatocellar carcinoma tissues of 12 cases with hepatocellar carcinoma ex-pressed PML protein ,and there was significant difference of PML protein expressed among 12 cases suffer with hepatocellar carci-noma .hepatocellar carcinoma cell lines ,such as HuH7 ,HepG2 ,Hep3B ,SMMC-7721 and MHC97H all expressed PML protein ,and there was little difference of PML protein expressed among hepatocellar carcinoma cell lines .The PML protein expression of HuH7 ,HepG2 ,Hep3B ,SMMC-7721 and MHC97H cell after 72-96 h treated with 0 .25 μg/mL of As2O3 significant decreased . Conclusion Hepatocellar carcinoma tissue and cells may express PML protein ,and As2 O3 may regulate this protein expression as well .PML protein may be the target molecule of As2 O3 treating HCC .