Dendrimers are widely used for biological applications. However, their effect on protein stability has not been studied extensively. Typically, charged cationic dendrimers such as PAMAM dendrimers tend to destabilize proteins due to the cooperative binding of surface groups to the protein surface. We have studied the effect of PAMAM dendrimer salt solutions on protein stability both experimentally and computationally. We show that the effect of dendrimers on protein stability depends on the choice of counterion (e.g., dihydrogen phosphate salts reduce the rate of protein aggregation, while chloride salts increase the rate of protein aggregation). In the presence of dihydrogen phosphate and sulfate counterions, the binding of dendrimers to the protein surface is limited (when compared to chloride and thiocyanate), which enhances the conformational stability of proteins. To the best of the authors’ knowledge, this is the first study that has shown that PAMAM dendrimer salts can significantly suppress the aggregation of proteins.