Smith has scored almost 14,000 runs since his 1990 first-class debut
Ben Smith has stepped down as captain of Worcestershire.
Smith, who replaced Graeme Hick in 2003, told New Road bosses of his decision during the current Championship match against Northants.
Steve Rhodes will take over for the remainder of the game, but a permanent replacement will be announced later.
Smith said: "I've come to this decision because I want to concentrate on my own form and help Worcestershire be successful for the rest of the season."
Coach Tom Moody said he and Smith had held discussions in the days leading up to the announcement.
"I'm sure Ben has caught a few people by surprise but we have talked about it over the last couple of days and I'm sure he has been thinking about it longer than that," Moody told BBC Sport.
"The captaincy was affecting his batting and he wants to focus on that.
"We fully support his decision and will appoint a new captain after this match."
Smith, 32, formerly of Leicestershire, has nevertheless scored 824 runs this Championship season at an average of 59.
He led Worcestershire up from Division Two last year and into this year's C&G Trophy final against Gloucestershire, which will be played at Lord's on 28 August.