<p>Laser light scattering (LLS) and conductivity experiments were performed to investigate the effect of counterions on the conformation of polycarboxylate comb-like copolymers (PCEs) in aqueous solutions. The addition of monovalent ions (i.e., Na<sup>+</sup> and K<sup>+</sup>) to dilute polycarboxylate comb-like copolymer solutions induced a slight shrinking of the molecular chains because of the screening of electrostatic intramolecular repulsion. Varying complexation phenomena, such as the formation of intramolecular complexation at certain Ca<sup>2+</sup> concentrations and a transition between intermolecular and intramolecular complexations at different Ca<sup>2+</sup> concentrations, were closely associated with Ca<sup>2+</sup> concentration. Therefore, Ca<sup>2+</sup> exerted a more complex influence on the conformation of PCEs with side chains containing polyethylene oxide (PEO) with different grafting densities. In addition, various combination types of Ca<sup>2+</sup> with carboxylic groups were confirmed by theoretical simulation.</p