Abstract: Microcystins (MCs) are hepatotoxins which inhibit the activity of protein phosphatase 2A (PP2A) notably.The cells were incubated with different concentrations of MC-LR to determine the effect of MCs on PP2A in HL7702respectively for 24h. The mRNA and protein levels of PP2A subunits were detected. Furthermore, the activity of PP2Awas assayed after 3h, 6h, 12h and 24h exposure. The protein levels were not changed significantly except B55α whichdecreased concentration-dependently and significantly in 1000 nmol/L. For mRNA levels, 15 subunits increased in 100nmol/L group, whereas 7 subunits in 500 nmol/L group and 6 subunits in 1000 nmol/L group decreased. The activity ofPP2A was inhibited significantly and concentration-dependently after 6h exposure while there were no changes in 3, 12and 24h exposure. In conclusion, MC-LR affects the transcription of PP2A subunits after 24h exposure, without concomitantchanges in the interrelated proteins. Exposure time might be a determinant when considering the effect ofMC-LR on PP2A activity.