Jonidan (序二段) is the second lowest division in the professional sumo ranking system of six divisions for wrestlers. Unlike the divisions above it, there is no fixed general number of wrestlers in the division although it is the largest division with commonly around 300 ranked within it. As a result of the numbers, and the fact that the wrestlers fight only seven times during a tournament, a kettei-sen play-off tournament on the last day is normally required to determine the division champion.

Wrestlers in this division are forbidden from wearing overcoats over their thin cotton yukata, even in winter and must wear geta on their feet. They often also pick up many of the more mundane chores within the training stable in which they live.