A pet access door that is adaptable for disposition within a door frame havingtwo vertical doorjambs and a horizontal door casing. The door includes a first panel and asecond panel arrangedin a parallel, substantially overlapping relationship to the first panel. Thefirst and second panelsare configured to move outwardly to an expanded engagement position in orderto engage the petaccess door against the two vertical door jambs of the door frame. A securingapparatus isconfigured to removably secure the first panel and second panel to the doorframe. A pet accessdoor assembly is mounted within the second panel and allows accesstherethrough when the firstand second panels are in the expanded engagement position.
