The 28-year-old joined The Crazy Gang from Premiership side Fulham back in July 2000 but spent two months on loan last season with The Shrimpers and Selley will have a chance to further impress the Essex club during the early stages of the new season.
The midfielder was pleased to return to Southend and get a chance of regular first team football with manager Rob Newman's side.
Selley told the Wimbledon official website: "The opportunity came up to go to Southend again after I'd been there last season, and I thought it would be a better situation playing there in front of a few thousand rather than in Wimbledon's reserves.
"I've enjoyed my time at Roots Hall so far, they are a good bunch of lads, and I'm pleased to be playing first-team football again."
Meanwhile, The Shrimpers have also signed former Wimbledon defender Neil Jenkins on a one-year deal after an initial trial with the Division Three side.
The 20-year-old can play on the left side of midfield as well as in the back-line and Newman is delighted to add such a versatile player to his ranks for the new season.
Newman told the Evening Echo: "Neil has done very well since he linked up with us for pre-season and I'm glad it has worked out for him here.
"He gives us added flexibility as he can play anywhere down the left-hand side, which further strengthens our squad."
The Southend boss added that he is also planning to complete the signatures of midfield youngsters Jay Smith and John McGrath on month-long deals.
The duo have been on trial from Aston Villa and look set to prolong their stay with the Essex club.
