Anionic and cationic block copolymers containing different fractions and chain lengths of poly(ethylene glycol) (PEG) blocks were synthesized and characterized. Polyelectrolyte complex (PEC) formation between these copolymers and homopolyelectrolytes and the stability of these complexes in salt solutions were studied by static and dynamic light scattering and laser Doppler electrophoresis. Complex formation led to particle systems with a high level of aggregation. For the anionic copolymers, even a low content of the short PEG block (M = 2 kDa) stabilized the PECs near the 1:1 mixing ratio. Independent of the content of the neutral block, the stability of complexes with short PEG blocks with regard to subsequent addition of salt was very low. When copolymers with long PEG blocks were used in PEC formation, high salt stability was observed.