The present invention relates to a bearing unit for protecting the blade of a grass mower and preventing a cover plate from being damaged due to a driving force of a driving motor, and a protection cover for a grass mower using the same. The protection cover for a grass mower according to the present invention, comprises: a bearing coupled with a driving shaft of a driving motor to be positioned at the lower portion of a blade so as to protect the blade mounted to the driving shaft of the driving motor, which is mounted to a working stand a cover member coupled with the bearing and having a protection plate formed in a diameter relatively larger than the rotation diameter of the blade so as to protect the blade a rotation supporting means for supporting the protection plate to be rotatable in a predetermined angle when the protection plate is applied with a rotational force by the driving force of the driving motor and an interval keeping member for keeping an interval between the blade and the protection plate to be a predetermined distance or more, thereby preventing the protection plate from colliding with the blade by being bent. The bearing unit according to the present invention may increase the compatibility of the blade of the grass mower and the protection cover for the grass mower and effectively block the introduction of impurities into the bearing during mowing, thereby preventing the lifespan of the protection cover for the grass mower from decreasing due to the damage to the bearing.
