Ted William's longest home run in Fenway Park was 502 feet, but I don't know if that was his longest home run ever.
The longest home run was made by Ryan Howard. 536 ft.
Ronnie Green of the KC Royals hit the longest home run at Fenway Park in 1987
The longest home run of 2009 belongs to Waldemar Balentien of the Cincinnati Reds. It was measured at 495 ft.
507 feet by prince fielder
525 feet
603 ft
760 ft.
Mickey Mantle
Canseco
405'
The longest home run that can be verified was hit by Babe Ruth. It went an estimated 575 feet. Many hitters have hit home runs that may be longer, but the distance was not or could not be verified.