Robert Croft has resigned as Glamorgan captain and has been replaced by batsman David Hemp.
Croft has two years left on his Glamorgan contract
Croft, 36, took over as captain in 2003 and led the side to the National League title in his first season in charge.
But Glamorgan were relegated from Division One of the County Championship last year, and have struggled with a young side again this season.
"I've always believed each person who holds the position would know the right time to pass over the reins," he said.
"I have held the position with unimaginable pride and experienced great moments both on and off the field.
"In standing down at this time it gives the club the opportunity to make an appointment for the longer term.
"I will, of course, give David my 100% backing in the remainder of my time in the club and I will do all in my power to ensure my own game reaches the standards I set for myself.
"I want to place on record my thanks to the coaching staff, players, groundstaff and office staff who have supported me and to the members of the club for their unstinting loyalty."
All-rounder Croft, who has two years left on his contract, has enjoyed one of his best seasons with ball by taking 63 wickets in the County Championship.
Having been senior professional I know the difficulties that Robert has had to deal with and his reasons for standing down
But Glamorgan have managed just two Championship wins from their 15 games so far, leaving them one from bottom with one game remaining.
The Welsh county have also won just two of their NatWest Pro40 Division One games and are in danger of being relegated.
Hemp made his Glamorgan debut in 1991.
The 35-year-old, who was born in Bermuda, left to join Warwickshire in 1997 but returned to Sophia Gardens four years later.
The former England A international said: "I am delighted to have been given the opportunity to captain Glamorgan, though naturally these are not the circumstances I would have wished for.
"Having been senior professional I know the difficulties that Robert has had to deal with and his reasons for standing down.
"The fact that he has managed to have such a good season individually speaks volumes for his character, but we're all grateful to him for what he has done.
"I will relish the chance to lead the side."
Glamorgan chief executive Mike Fatkin said: "We are fortunate to have someone of David's experience and ability to take over.
"He will have his own ideas as to how to approach the captaincy.
"We will be talking with him in the coming weeks to ensure that we are providing the right framework of off-field support in order to enable him to start bringing about an improvement in the team's performances with effect from next season."
Hemp's first game in charge will be in Glamorgan's final Pro40 League match this season away to Lancashire next Sunday.