Abstract: Effects of inorganic salts, fiber constitution, and pH on the zeta potential of paper stock were examined with the design of experiment (DOE). The results showed that the zeta potential increased along with the increase of inorganic salts concentration. Comparing to Ca2+ and Na+, Al3+ gave the greatest influence on the zeta potential of stock system. The zeta potential decreased along with increasing both the ratio of hardwood pulp and pH. The first pass retention (FPR) reached the maximum when the zeta potential was near to zero.