Iwatsuki-ku is one of ten wards of the city of Saitama, in Saitama Prefecture, Japan, and is located in the northeastern part of the city. As of 1 March 2021, the ward had an estimated population of 112,862 and a population density of 2,300 persons per km2. Its total area was 49.17 square kilometres (18.98 sq mi).

Iwatsuki Domain was a feudal domain under the Tokugawa shogunate of Edo period Japan, in Musashi Province, Japan. It was centered on Iwatsuki Castle in what is now part of Iwatsuki-ku, Saitama.