Dextran esters of different amino acids (glycine, $\beta $-alanine, L-ornithine, L-lysine) are investigated regarding their pK$_{a}$ values by potentiometric titration. The pK$_{a}$ values of the dextran derivatives are generally dependent on the position of the amino group in relation to the ester group, i.e. the nearer they are located in the molecule, the lower the resulting pK$_{a}$ values are, L-ornithine ester being the exception. An influence of the polymer backbone is ruled out. Stability against hydrolysis at different pH values and over longer periods at constant pH value is measured by potentiometric and polyelectrolyte titration. The $\beta $-alanine ester shows slowest hydrolysis at alkaline pH values, starting at a pH value of 8. The esters investigated are polycations at physiological pH values; thus, the charging properties are essential for using these esters as nonviral vectors in gene delivery.