The　relationship　between　saturated　adsorption　amount　(A(s))　and　pH　and　the　relationship　between　saturated　adsorption　amount　(A(s))　and　ζ　potentials　for　two　cationic　dyes　and　three　anionic　dyes　on　activated　carbon　have　been　studied.　It　has　been　found　that　A(s)　of　the　dyes　on　activated　carbon　is　correlated　with　the　electrostatic　forces　between　charges　on　the　carbon　surface　and　ionic　dyes.　The　experimental　results　showed　three　distinct　states　regarding　the　effect　of　ζ　potential　on　carbon　surface.　In　the　neutral　potential　state　where　ζ　potential　is　nearly　zero,　the　electrostatic　interactions　between　the　carbon　surface　and　the　dyes　are　negligible　and　the　adsorption　forces　are　mainly　dispersion　forces.　Therefore,　pH　has　no　effect　on　A(s).　In　the　positive　or　negative　potential　states,　there　exists　the　electrostatic　attractive　or　repulsive　forces　between　activated　carbon　and　the　ionic　dyes.　The　adsorption　forces　are　the　sum　or　difference　of　dispersion　and　electrostatic　forces.　The　adsorption　amount,　A(s),　changes　with　ζ　potential.　The　different　types　of　adsorption　forces　in　the　three　potential　states　reveal　the　mechanism　of　adsorption　for　the　dyes　on　activated　carbon.　The　conclusion　is　further　supported　by　the　kinetic　and　thermodynamic　parameters　that　were　calculated　from　the　experimental　data.