Baillie Gifford manager Andrew Strathdee is to step down from the firm next June after 24 years.
Strathdee joined Baillie Gifford as a graduate in 1995 and is currently an investment manager in the UK equity team, having previously worked on the firm's Asia and European equity desks.
He is manager of the £192m British Smaller Companies fund, which he has run since 2013.
Over the last three years, the fund has returned 23%, according to FE, versus returns of 47.2% by the IA UK Smaller Companies index.
A spokesperson for Baillie Gifford confirmed a successor for the fund would be announced in due course.
There have been several departures of longstanding managers from the firm this year.
In January, Sarah Whitley, head of the Japanese equity team, Stephen Rodger and Ken Barker, both partners in the firm's fixed income area and Pete Cooke, partner with responsibility for clients in the long-term global growth strategy, announced they would retire on 30 April.
Meanwhile, US Growth trust deputy manager Andrei Kiselev left the firm after a decade in May, shortly after the trust had launched. He was also a named manager on the firm's £1.5bn American fund.
Risk to retail investors
Latest news and analysis
Taking up non-exec role
Following 2016 thematic review