Abstract: A modular collapsible tank trailer railing assembly for connection to a catwalk on the top of a tank on a tank trailer, the modular collapsible tank trailer railing assembly including a base member connected to the catwalk, an upper rail, a middle rail located between the upper rail and the base member, a plurality of posts pivotally connected to the base member, the middle rail, and the upper rail, a handle for rotating one of the plurality of posts to raise and lower the upper rail and the middle rail, and a spring for biasing one of the posts toward the upright position.