Revenue in the West End office investment market soared 35% to £348.7m last month.
Of the deals in May, seven were for transactions over £10m, according to research from Strutt & Parker.
Sales in May totalled £348.7m, compared to £258.8m in May 2012.
A lack of stock on the market, has fuelled competitive bidding and led to a number of assets being sold above asking price.
In the lettings market, Strutt & Parker said that as at the end of May, demand has risen minimally from May 2012, to 5m sq ft.