The invention provides a sheet processing apparatus and an image forming system. A sheet processing apparatus includes: a loading tray on which a sheet is loaded; a pair of ejection rollers that eject the sheet to the loading tray and in which a pair or roller members are configured to be able to contact with and separate from each other; a pair of shift rollers that is provided upstream of the pair of ejection rollers in a sheet conveyance direction, are movable in a sheet width direction that is a direction perpendicular to the sheet conveyance direction, convey the sheet towards the loading tray, and performs a shift operation of shifting the sheet to a different position in the sheet width direction; and a control unit that performs control to change, based on sheet information, a shift operation timing of the sheet by the pair of shift rollers and a contacting and separating timing of the pair of ejection rollers.