Abstract: An apparatus for adjusting folding jaws of a folding jaw cylinder having an axle on which a first cylinder part supporting at least one uncontrolled folding jaw and a second cylinder part supporting at least one controlled folding jaw are provided so as to be rotatable in opposite directions. The apparatus includes an adjusting spindle in one end of the axle of the folding jaw cylinder, two slide members, and a housing attachable to the axle at an end face of the cylinder parts and having two oppositely disposed two housing arms with radially directed guides. Each slide member being slidably arranged in a respective housing arm guide and have one end that engages with the adjusting spindle and another end that is engageable with one of the cylinder parts. Sliding pairs are provided for allowing sliding of the slides within the housing arms in a radial direction.