Abstract: Objective To explore the changes of mitochondrial transmembrane potential(m)in V79 cells caused by hydroquinone with fluorescent JC-1 and the protection of lipo ic acid.Methods V79 cells were cultured in vitro,then treated with lipo ic acid and hydroquinone into different groups for twenty-four hours.The levels of mitochondrial transmembrane potential were analysed by flowcytometry.Results Normal V79 cells had a high m(1.12),and JC-1 agg regates were for med in the inner membr ane of mitochondria and emitted orange-red fluorescence.50mol/L and 100 mol/L hydroquinone caused the decrease of m,and JC-1 aggr egates were disso ciated to monomer which emitted green fluorenscence(0.22 and 0.03).Treatment with lipoic acid alone didn't change them,but it could effectively protect V79 cells from hydroquinone tox icity(0.79 and 0.63).Conclusion The results showthat lipoic acid can inhibit decrease of mitochondr ial transmembrane potential of V79 cells damaged by hydroquinone.