The German finance industry believes Frankfurt would emerge as a "major winner" if the UK votes for a so-called Brexit.
A survey of 400 businesses in the sector also found support for the London Stock Exchange-Deutsche Boerse merger.
But there are concerns about the headquarters of the holding company created by the merger being based in London rather than Frankfurt.
Goethe University's Center for Financial Studies found 63 per cent of companies surveyed are “fundamentally in favour” of the merger.
However, nine per cent support the deal unreservedly and 25 per cent are against the merger no matter what.
Under the terms of the merger, the holding company would be headquartered in London.
Some 57 per cent of participants said the consequences of the holding company being based in London would be negative, and this increased to 64 per cent in the case of a Brexit.
Some 18 per cent of respondents, meanwhile, only view the merger positively if the UK decides to remain within the EU.
Professor Volker Bruhl, managing director of the Center for Financial Studies, said: “The financial industry is convinced by the industrial logic of the merger, although negative impacts on the Financial Centre Frankfurt are foreseen if the holding is based in London.”
On the widespread effect of a Brexit, 82 per cent of those surveyed believe the UK would be “hit hard”, with 48 per cent predicting a negative impact on the EU. And 69 per cent said they would expect Frankurt to emerge as a “major winner” in the case of a Brexit.
Hubertus Vath, managing director of Frankfurt Main Finance e.V, said: “Of course we are not in favour of a Brexit. It would not only be detrimental for Great Britain, but also Germany and Europe as a whole.
"But should it come to pass, it would clearly be an opportunity for Frankfurt as a Financial Centre, as confirmed in the survey.”