The F1 business of Williams Grand Prix Holdings made a loss of £5.6m, up from £4.6m in the first half of 2012.
However, the wider group, which includes engineering and power concerns, as well as outside partnerships, reduced its overall loss.
Founder Sir Frank Williams said the firm was well placed to make progress.
So far this season, the Williams F1 team has only managed to win one point on the track after 12 races.
"The 2013 Formula 1 season has not brought the sort of results expected of a team with our history and pedigree," Sir Frank said.
"We have made strong personnel changes this year that will aid in returning us to winning ways."
He added that the team had announced a total of nine new sponsorship acquisitions, renewals and upgrades for 2013, and had a strong pipeline of potential sponsors in place for 2014.
The F1 business recorded a turnover of £43.5m, almost unchanged on the first half of 2012 of £43.4m.
Williams Advanced Engineering, the division of the group that commercialises Formula 1-derived intellectual property and know-how, recorded a turnover of £11.2m, down from £20.2m.
The firm attributed this to a reduction in pass-through contracting work.
Profits for the division rose to £4.5m, from £3.7m previously.
Overall group turnover dropped to £57.7m from £64.9m in the first half of 2012, but losses dropped to £2.7m from £3.1m previously.
Williams are one of the most successful teams in F1, but they have slipped from the pedestal they occupied when they dominated the sport for much of the 1980s and 1990s.
They have not won a championship since 1997 and last won a grand prix in 2012, when Pastor Maldonado won the Spanish Grand Prix, their first victory since 2004.
In recent years, they have struggled to raise the budget required to compete at the front.
The Williams Formula 1 business saw losses widen in the first half of this year as the firm continued to suffer on the track.