A spin label has been covalently attached to the weak polyanion poly(ethylene-alt-maleic acid) (P(E-alt-MA)) to study the segmental dynamics of the polyanion backbone in polyelectrolyte complex coacervate phases formed with oppositely charged polycations such as poly(diallyldimethylammonium chloride) (PDADMAC), linear poly(ethylenimine) (1-PEI) and poly(allylamine hydrochloride) (PAH) by continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy. The segmental rotational mobility of the spin-labeled polyanion has been determined by the simulation of the line shape of the experimental CW EPR spectra using the microscopic order/macroscopic disorder (MOMD) model of restricted rotational diffusion. The study has shown that the segmental mobility of the polyanion backbone in the coacervate phases decreases in the sequence PDADMAC > 1-PEI > PAH. The nature of the ion pairs formed between the oppositely charged polyelectrolytes has a strong impact on the dynamics of the polyanion.