Chlorine dioxide has an excellent ability to sterilize and deodorize and is harmless to humans. However, it is very unstable and explosive as it is highly concentrated, thus its use in the air clean filed has been limited. Therefore, there is a demand to develop the system to produce a low concentration of chlorine dioxide sustainedly. Here, for a first step in the development of the system on the sustained production of chlorine dioxide, the use of polymer hydrogels was investigated. P(MMA-co-HEMA) hydrogel particles were prepared via dispersion photopolymerization and sodium chlorite and citric acid were loaded respectively in the hydrogel particles. When sodium chlorite and citric acid were reacted with not loaded in the hydrogels, rapid production of chlorine dioxide occurred and the concentration of chlorine dioxide decreased over time. However, when sodium chlorite and citric acid were loaded respectively in the hydrogel particles and reacted, chlorine dioxide was produced slowly and sustainedly because the release of sodium chlorite and citric acid from the hydrogels delayed the reaction between them. The result shows that the use of P(MMA-co HEMA) hydrogels has the potential to develop the system on the sustained production of chlorine dioxide.