The influence of viscosity modifying admixtures(VMA) and superplasticizers and mixing of these two agents on zeta(ζ) potential of cement pastes(fresh) were analyzed using the ZetaProbe instrument. The experimental results show that since cement grains adsorb VMA or superplasticizer molecules, the ζ potential of cement pastes with VMA or superplasticizer decreases. The ζ potential of cement pastes with both VMA and polycarboxylic superplasticizer(PC) shows that cement grains primarily adsorb PC molecules, whereas the absolute value of ζ potential of cement pastes with both VMA and naphthalene formaldehyde condensate superplasticizer(NF) is lower than that with only NF. To add PC into cement pastes with VMA or to add VMA into cement pastes with PC will result in the ζ potential increase. The ζ potential of cement pastes with NF increases from -8 mV to -3 mV as VMA is added in. However, it is still lower than that with both VMA and NF. The ζ potential of cement pastes with VMA decreases as NF is added in, and the ζ potential absolute value is higher than that with both VMA and NF when the use level of NF increases to a certain value.