A saddle mounting device includes a support member having a mounting portion formed thereon. A lower base is connected with the support member. The lower base has two guiding flanges diametrically formed thereon. Two gaps are respectively defined between the two guiding flanges. The lower base has two first engaging grooves defined therein. An upper base is movably connected with the lower base. The upper base has two sliding rods formed thereon for sliding along the two guiding flanges and are guided into the two gaps. The upper base has two second engaging grooves defined therein for corresponding to the two first engaging grooves. A fastener connects the support member with the lower base and is screwed with the upper base. The upper base is simultaneously moved relative to the lower base by a rotation of the fastener.