A sight includes a main body, an erecting unit and a compensating mechanism. The compensating mechanism includes a fixing unit, a cover and an switching unit. A compensating mechanism for a sight includes a base unit, a transmission unit, an adjusting cap, a movable unit and a lock unit. The adjusting cap is located in a first position when the adjusting cap is locked by the lock unit. The adjusting cap in the first position can be rotated in a second direction or in a third direction opposite to the second direction when the lock unit is moved in a first direction to release the adjusting cap. The adjusting cap stops in a second position when the adjusting cap is rotated in the third direction so that the movable unit is propped against an end of a groove of the adjusting cap.