A door opener with an anti-loose linking unit includes a driving device and a linking unit disposed between the driving device and the door. The driving device includes a motor and a first transmission member operatively connected to the motor. The linking unit includes a first push rod connected via a connecting screw to the first transmission member, permitting joint pivotal movement. An anti-loose member is non-rotatably mounted on the first push rod. Ahead of the connecting screw is non-rotatably coupled with the anti-loose member. Thus, the connecting screw cannot rotate relative to the first transmission member and the first push rod, reliably preventing the first push rod from disengaging from the first transmission member.