Leadbitter, named regional contractor of the year in the 2000 Building Awards, has 300 staff. It has offices in Oxford, Bristol and Bracknell, Berkshire.
Most of the firm's business is in the public sector, in social housing, schools, healthcare and leisure.
Leadbitter managing director Bob Rendall said this week that talks on the deal were going on. Heijmans is interested in buying Leadbitter for cash.
Rendall said: "It has put a proposal to us – it is by no means a done deal. It's very flattering for us to get the approach. The deal will be decided upon one way or another in the new year."
Rendall added that the future of the firm's employees was his priority. He said: "We will be insisting we maintain our independence."