A locking drain filter for floor drains with drain wells is provided. An upper filter portion has external dimensions that allow the upper filter portion to be inserted into a drain line at the bottom of the drain well. A lower filter portion has first external dimensions that allow the lower filter portion to be inserted into the drain line and second external dimensions that allow the lower filter portion to be inserted into the upper filter portion. A compressible gasket has external dimensions that allow the compressible gasket to be inserted into the drain line when the compressible gasket is in an uncompressed state and internal dimensions that allow the compressible gasket to be placed over the second external dimensions of the lower filter portion. A compression device applies a compressive force to the upper filter portion and the lower filter portion, and if the upper filter portion, compressible gasket, and lower filter portion have been inserted into the drain line prior to the application of the compressive force, the compressible gasket is compressed by the upper filter portion and the lower filter portion and expands radially so as to lock the upper filter portion and the lower filter portion into the drain line.