A mop strainer has a bucket, a driving unit, a transmission unit and a draining unit. The driving unit and the transmission unit are received in a pedal mount of the mop strainer. The driving unit and the transmission unit are driven by stepping on the driving unit, so as to rotate the draining unit and drain a mop. The driving unit has a reinforced sector wall and a limit slot to limit the stroke in operation. The draining unit has a water guard to prevent drained water from sputtering out and the water guard further has a mop gripper for holding the mop. Given all these features, the present invention is more robust and can be operated and stored more conveniently and practically.