The effect of condensates of phosphates on the preservative activity of the food additives, using eight micro-organisms, has been studied by the agar dilution method. It was found that condensates of phosphates increased the food preserving action of almost all of preservatives and they acted as a synergist for the action of almost all of preservatives. Disodium dihydrogen prrophosphate acted as the strongest synergist in the experiment. But sodium tripolyphosphate anhydrous, sodium poly-phosphate, sodium tripolyphosphate and sodium hexametaphosphate acted as a inhibitor for action of some preservatives on some orgnisms. The preservatives were sodium dehydroacetate (DHA), potassium sorbate and NaNO$_{2}$ etc. The action of sodium meta-phosphate on the preservatives produced a mean difference by their origins. It was supposed that such a difference was produced by the difference of amount of impurities that were contained in sodium metaphosphate, It was also supposed that the does of the preservatives could be reduced by addition of condensates of phosphates, acting as a synergist for the action of almost all of the preservatives.