Jonokuchi (序ノ口 or 序の口) is the lowest division. All wrestlers, apart from those who have had successful amateur careers and are given special dispensation to enter makushita directly, start in this division. In addition to the new wrestlers the division tends to consist of other recent recruits to sumo wrestling as well as some older wrestlers who have fallen to the bottom of the ranks due to prolonged injury.

A new wrestler's initial position in the jonokuchi division is determined by his performance in mae-zumo, a tournament held among new wrestlers at the time of the grand tournament before they are ranked for the first time. The jonokuchi division varies in size and typically includes between 40 and 90 rikishi, with the high mark being reached for each May tournament as the number of recruits appearing in mae-zumo is generally largest during the preceding March tournament, when the Japanese school year ends. As with the other lower divisions, wrestlers only compete in seven bouts over the course of the tournament. Jonokuchi is the only division in which a wrestler can be promoted even with a losing record, and promotions to the next highest jonidan division with a losing record are not uncommon. The word jonokuchi is also used as an expression to describe when something has just begun.

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