Newcastle have recorded a loss of £6.3million for the past half-year.
The pre-tax loss is published in the club's interim results for the six months ending January 31, 2006.
This compares to a profit of £9.7million over the same period last year.
The losses are principally attributed to a fall in overall revenue fell from £49.5million to £43million due to the club having six fewer fixtures in all competitions.
Newcastle also invested significantly on players during the period, signing Michael Owen, Albert Luque and Nolberto Solano.
Profit before player trading was recorded at £2.7million, down from £8.5million on the same period last year.
Manager Graeme Souness also parted company with a club after disappointing results in the first half of the season.
Chairman Freddy Shepherd admits the investment has not been reflected in performances on the field but is pleased with the progress under caretaker manager Glenn Roeder.
Roeder is in the temporary charge of the team until the end of the season and has lifted them to 10th in the Premiership.
Shepherd said: 'The current season has been disappointing with performances on the pitch falling well below the level we expected.
'Since his appointment as acting team manager, Glenn Roeder, capably supported by Alan Shearer, has overseen a significant improvement in team performances.'
Shepherd added: 'We want this positive trend to continue, while our search for the best possible team manager takes its course.'