Contractor pays £8m on ground engineering firm Pennine Group and £9.7m on signalling contractor SBB.
Balfour Beatty has bought two new companies for a total of about £18m.
It has paid £8m for UL ground engineering business Pennine Group, which is based in Bacup in Lancashire and employs 130 staff.
In the year ended March 2005 Pennine made a £1.5m operating profit on a £16m turnover.
In a second acquisition Balfour Beatty bought German signalling contractor SBB for Euro 14m (£9.69m).
SBB operates predominantly in the former East Germany, but has extended its presence into the West.
The company is based in Stassfurt near Leipzig and employs 85 staff. In 2004 it achieved a Euro 10m turnover.