Latest group results for the international giant reveal a construction operating loss of £393.3m compared to an operating profit of £64.8m last time as turnover fell £2.34bn to £9.72bn.
Bouygues said: “The decrease was entirely attributable to Covid-19, the impact of which was estimated at -€530 million (£477m) over the period.
“The Covid-19 pandemic strongly affected the construction businesses’ financial results in first-half 2020.
“After reaching a low point in April, the construction businesses returned to profitability in June 2020.”
Martin Bouygues, Chairman and CEO of Bouygues, said: “The long-term trends on which the Group relies remain buoyant, despite the current crisis.
“After a challenging first half of the year, our fundamentals and our strategy should enable us to return to growth in all three sectors of activity.”