Objective      To determine the effect of arsenic trioxide (As

2

O

3

) on the proliferation and differentiation of human liver cancer cell line HuH7 and its CD13

+

CD133

+

liver cancer stem cells (LCSCs).       Methods      CD13

+

CD133

+

LCSCs was sorted from HuH7 cells by fluorescence activated cell sorter (FACS). MTT assay and EdU incorporation was used to analyze As

2

O

3

stimulation in the proliferation of HuH7 cells and CD13

+

CD133

+

LCSCs. FACS was used to detected HuH7 cells’ apoptosis on the third day and fifth day stimulated by As

2

O

3

and HuH7 cell circle on the third day. Expression of promyelocytic leukaemia (PML) protein was detected by Western blotting. The sensitivity of HuH7 cells to pirarubicin (THP) and formation of tumor sphere was observed.       Results      As

2

O

3

at low concentration induced the proliferation in HuH7 cells and CD13

+

CD133

+

LCSCs in the early stage (within 5 d)

and that at high concentration suppressed CD13

+

CD133

+

LCSCs proliferation. Although As

2

O

3

did not block the circle of HuH7 cells

it had reduced cells at G

0

/G

1

phase by 2.32%. After 3 days’ treatment of As

2

O

3

the apoptotic rate of HuH7 cells was 8% to 9.5%

similar to the cells without treatment

but the rate was increased to 12% to 15% in 5 d after treatment. As

2

O

3

of 1.0 μg/ml resulted a higher apoptotic rate than that of 0.5 μg/ml in the late stage. As

2

O

3

enhanced HuH

7 cells’ sensitivity to THP

and reduced CD13

+

CD133

+

LCSCs’ capacity to form tumor sphere. PML protein was expressed in the HuH7 cells

which was down-regulated by As

2

O

3

.       Conclusion      Low concentration As

2

O

3

enhances the proliferation of HuH7 cells and CD13

+

CD133

+

LCSCs

induces apoptosis in HuH7 cells

and improves CD13

+

CD133

+

LCSCs differentiate. The effects might be mediated by PML.