An improved fluid filter assembly with a replaceable filter element having a frame, channel shaped in cross-section defining a shallow box with an upstream and downstream opening therein to permit fluid flow therethrough and a foraminous filter supporting member adjacent to one of the openings; a fibrous filter mat covering the foraminous member and having marginal portions extending into the channel shaped frame; and, a resilient endless retainer removably engaging the fibrous filter mat by nesting in the channel shaped frame, the resilient endless retainer being an endless loop pivotally attached to the exterior of one extremity of the channel shaped frame, the loop including an inwardly extending groove portion at a position opposite the portion of the loop which is pivotally attached to the channel shaped frame, the inwardly engaging portion being adapted for removable engagement with the interior of the channel shaped frame.