The Deputy Prime Minister hopes to secure deals worth £500 million and began his visit by announcing a series of contracts had already been signed with Turkish companies to help revive the UK's economy, creating dozens of jobs.
The Liberal Democrat leader said: "It's fantastic to be announcing new jobs for the UK and such an impressive set of deals for British businesses. Turkey is Europe's seventh largest economy and is one of the world's largest markets.
"My main aim this week is to ensure that more UK firms can capitalise on the economic opportunities Turkey offers."
Deals already agreed include Turkish company HDM Steel Pipe opening a £7 million factory in Cardiff, creating 38 jobs, and Wolverhampton-based Concept Steels signing a £5 million contract with a Turkish firm to export alloys, metals and components for the oil, gas and chemical industries.
Meanwhile, Istanbul-based hospital group Florence Nightingale will set up its European headquarters in London, creating eight jobs and investing £100,000.
Mr Clegg, who will visit Ankara and Istanbul with Conservative Business Minister Michael Fallon and 18 top executives on the two-day trip, added: "We have an ambitious aim to double bilateral trade by 2015. "It has increased by 40% since 2009, so we are making good progress towards the target, and this visit will bring us even closer."