Jonokuchi (序ノ口) is the lowest division in the professional sumo ranking system of six divisions for wrestlers. 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 injury.

A new wrestler's initial position in the Jonokuchi division is determined by his performance in mae-zumo a sort of entry tournament held among new wrestlers at the time of the grand tournament before they are first ranked.

It is also used to describe when something has just began.