The two FTSE 250 companies confirmed that they were in early stage talks, in separate statements to the stock exchange this morning.
As of 8.45am, shares were up 4.5% from Friday to 632p and shares were up 15% to 444.5p.
Informa's share price may reflect expectations that it will attract interest from other companies. It has already climbed in recent weeks amid rumours of interest from private equity firms such as Apax and Carlyle.
UBM's move comes five months after by Guardian Media Group and private equity firm Apax for £1bn.
A merger would bring together UBM titles such as Property Week, Music Week and Farmer's Guardian with Informa's Lloyd's List and wide range of academic journals. It would also include both company's extensive events, exhibitions and data businesses.
UBM and Informa both have presences outside the UK -- UBM is established in China, India and Brazil, while Informa is in the Middle East and Singapore.
The two companies would make a good fit, they are have roughly equal values: UBM has a market capitalisation of £1.5bn and Informa of £1.6bn.
Informa, however, has a large debt load after its £502m acquisition of market research company Datamonitor last May.
It is understood that the management line-up following the possible merger is not finalised.
Analysts have suggested that David Levin, chief executive of UBM, should take the reins with Peter Rigby, chief executive of Informa, as chairman.
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