The men's 400 metre freestyle event at the 1988 Summer Olympics took place on 23 September at the Jamsil Indoor Swimming Pool in Seoul, South Korea.
Prior to this competition, the existing world and Olympic records were as follows.
The following records were established during the competition:
Rule: The eight fastest swimmers advance to final A (Q), while the next eight to final B (q).
Note: All eight swimmers who qualified for the Olympic final swam faster than the Olympic record time.