A shower door assembly is disclosed comprising a stationary frame, a movable frame with a through hole, an upper frame, a lower frame, and an adjusting assembly. The adjusting assembly further comprises a fixing block disposed between the stationary frame and the movable frame and received in the stationary frame, the fixing block having a passage with a first rectangular cross-section, and rotating blocks received in the upper frame and the lower frame respectively and having a rotating handle and an adjusting shaft perpendicular to the rotating handle. The end of the adjusting shaft remote from the rotating handle has a second rectangular cross-section with dimensions identical to the first rectangular cross-section, and an engaging element is disposed on at least one surface of the adjusting shaft.