A lower arm mounting unit for a multi-link suspension system having a knuckle rotatably supporting a wheel, and first and second lower arms connecting the knuckle to a vehicle body, may include a pair of mounting protrusions formed to the knuckle, a first ball stud connecting an end portion of the first lower arm to the pair of the mounting protrusions, and a second ball stud connecting an end portion of the second lower arm to the pair of the mounting protrusions and the first ball stud by inserting the end portion of the second ball stud between the pair of the mounting protrusions, the end portion of the first ball stud, and the knuckle.