To study the regulation of bailong, a Chinese herbal anticancer preparation and hexamethylene bisacetamide (HMBA) on cyclin dependent kinase inhibitor P16 (CKI-P16) genes in human cancer cells.The expression of CKI-P16 in different human cancer cells treated by Bailong or HMBA under different condition, was examined using Northern hybridization, Western blotting assay, etc.After being treated by Bailong or HMBA, the P16 expression increased. This effect was closely related to co-regulation of cAMP-PKA and DAC-PKC signal pathway. When PKA pathway was blocked with PKA inhibitor, the P16 expression decreased, while PKC pathway was blocked, it enhanced.(1) The low P16 expression in G1 phase of cancer cell, as compared with that in S, G2 and M phases, might be an important factor responsible to the incompetence of P16 in inhibiting effectively the malignant change of cancer cell. (2) Mechanism of Bailong and HMBA on cancer cell proliferation inhibition might be correlated with the enhancement of P16 expression in G1 phase of cancer cells. (3) Regulation and expression of Bailong and HMBA on P16 showed the common character of Chinese and western medicine in regulating cancer cells. (4) This study elucidated that upstream of P16 was related to cAMP/PKC signal pathway closely.