The former Australia captain said the South African-born batsman, whose form was a rare bright spot on England's disappointing tour, ought to have stayed if there was any chance he could help his team into the finals.
Pietersen had his rib broken by a lifting delivery from Australian paceman Glenn McGrath at the Melbourne Cricket Ground on January 12.
An x-ray revealed a fracture that would keep him out of action for up to five weeks and the English management opted to send him home to ensure his fitness for the World Cup in the West Indies starting on Mar. 13.
However, Border said Pietersen acted too hastily by returning home.
''I've got to say he was on the plane before the x-ray came back,'' Border told Australian television.
''If he's got a broken rib, fair enough, but it wasn't displaced broken, it was just cracked and given two weeks' break he could be playing.
''With England a chance to scrape into the finals and he a key man. Too quick on to the plane for my liking.'' England have lost all but one of their six tri-series matches and need to beat Australia in Sydney on Friday and then New Zealand in Brisbane on Tuesday to have any realistic chance of qualifying for the three-match finals.