The release of heavy metals, for example, lead, cobalt, and copper, from industrial activities harms both human health and the aquatic ecosystem. One promising material to solve this problem is a smart hydrogel that can promote adsorption in response to temperature. In this study, we present a promising smart hydrogel of poly(N,N-dimethylacrylamide-co-N-isopropylacrylamide) (P(DMA-co-NIPAM)) as an adsorbent for heavy metal ions in water that has a thermoresponsive behavior. The swelling ratio showed the thermoresponsive behavior, with a decreasing swelling ratio with increasing temperature. The highest swelling ratio was possessed by DMA:NIPAM of 35:65 (mol%) and 3% MBA. The presence of heavy metal ions reduced the phase transition temperature (Tc) of P(DMA-co-NIPAM) hydrogel from 40°C to 35°C. Moreover, the adsorption capacity increased not only with the increasing initial concentration of heavy metal solutions, but also with the decreasing temperature at the pH optimum of 4.5 for Cu(II) and 5.5 for Co(II) and Pb(II). The increase in adsorption capacity of at least 25% at low temperature reveals the smart behavior of P(DMA-co-NIPAM) hydrogel as the adsorbent. The adsorption capacity of P(DMA-co-NIPAM) hydrogel decreased in the following order: Co(II) > Cu(II) > Pb(II), with the Langmuir model being the most suitable adsorption isotherm model. © 2026 Wiley Periodicals LLC.