Abstract: In a railway sleeper assembly, a pair of rail insulators (3) designed for use with a steel railway sleeper (1) which includes at the opposite sides of each intended rail location thereon a pair of openings (6) for receiving the respective stems (8) of a pair of shoulders (4), are each operatively disposed, when in use, between a foot of the rail (2) and the respective proximate shoulder (4). Each insulator (3) includes a member (11) which, when the insulator is in use, operatively extends below a top surface of the sleeper (1) and into the associated opening (6) so as to lie between the walls of that opening (6) and the stem (8) of the associated shoulder (4), thereby to retain the shoulder (4) in its operative position relative to the sleeper.