The invention relates to a barrier (100) suitable for installation in a sewage pipe and for preventing vermin from passing the barrier. The barrier comprising a support structure (101) with a first hinge (108) and a second hinge (109), a first shutter (102) pivotably mounted on the first hinge, a second shutter (103) pivotably mounted on the second hinge, and a locking mechanism comprising a first part (104) being a blocking mechanism, a second part (105) being formed as a protrusion. The locking mechanism is provided for keeping the second shutter (103) in a closed position, when the second shutter is tampered with by a vermin, e.g. a rat, trying to pass the barrier. This vermin barrier has the advantage of being reliable for preventing any vermin to pass the barrier, as the locking system within the barrier has a very optimal locking effect.