Mustoes pitched against a shortlist comprising Vallance Carruthers Coleman Priest, Grey London and St Luke's.
The four agencies were whittled down from a longlist of 12 by ISBA, in a pitch that has run for last three months.
The final shootout was between Mustoes and VCCP. The process was overseen by Kia Motors director of marketing Guy Jones.
"Mustoes won the pitch and retained the account by offering the best balance of quality, value and cultural fit with Kia," Jones said. "The response to our pitch process was outstanding and has confirmed the high level of interest and potential of the Kia brand."
The review was part of a shake-up of the company's suppliers, systems and procedures over the past 14 months following the UK firm's takeover by Korea's Kia Motors Corporation in August 2002.
Mustoes, which has held the business since mid-1999, is now working on a brand strategy and marketing programme for 2004 to increase awareness and intention to purchase of Kia's line-up of cars.
The company is launching three new models in 2004, including the Picanto, an all-new small car, which had its world premiere at the Frankfurt Motor Show in September.
It is thought that the media account, held by Starcom Motive, could also be up for review, although Kia has so far denied this.
There have also been reports that the company is looking for a direct marketing agency, but this has also been denied. Kia's direct marketing is currently handled by in-house agency Amethyst.
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