A multifunction office/fitness chair includes a backrest with an armrest and a seat connected with the backrest through a pivot. The backrest is also connected with a footrest through a footrest connection device. The backrest is able to rotate 90 degrees around the pivot, so that the chair can be switched among an office-chair state for work, a recliner state for exercise and a middle state for rest. A user can use the chair of the invention for work and for exercise in a bedroom or an office without limitations to access to equipment, location and time. Using the chair to exercise three to five minutes per day can help lose weight effectively.