The Mayor of London began his Japanese trade mission by waltzing in the aisles of a department store in Hankyu, Osaka.
The 51-year-old Tory danced with Charlotte Gooch, who is starring in a touring production of Top Hat.
The trade fair has been running since 1970. Dozens of British companies attend the promotional event, which brings in about £1.6 million over the course of a week.
Visitors from across Japan attend the event, where popular British produce, such as fish and chips and afternoon tea, are on sale.
The Press Association reports that Johnson said: "This is the third biggest economy in the world. It's one of our most important trading partners. Since the early 1980s it has been a massive investor in London. We are seeing more of it now and we want to encourage that."
Next stop Strictly? Boris Johnson performs a waltz with dancer Charlotte Gooch in a Japanese department store pic.twitter.com/Y05i7LzrLE— Sam Lister (@sam_lister_) October 13, 2015
Over the course of the three-day visit, Johnson will push for British companies to secure a share of £10 billion worth of contracts in the run-up to the Japanese Olympics and Rugby World Cup.
The MP for Uxbridge and South Ruislip added: "Tokyo has got the Olympics in just five years' time, they have got the Rugby World Cup in four years' time.
"This is a crucial moment for them in their procurement. They have got £10 billion worth of contracts going out.
"We think that British companies ought to be trying to compete, ought to be offering their services there."