Some 7,000 regular donors have stopped giving money to Oxfam following allegations of sexual misconduct against some of its workers in Haiti.
Oxfam GB chief executive Mark Goldring revealed the figures as he was questioned by MPs on the International Development Select Committee.
Asked how many people had stopped donating to the aid charity, Mr Goldring said: "About 7,000 individuals have cancelled a regular donation in the last 10 days."
He added: "Corporate sponsors at the moment are reserving judgement.
"They want to look at what we have done, what our policies and procedures are, how their relationship may have been compromised and what we're setting in place for the future."
During a session that lasted almost two hours, Mr Goldring was one of three senior Oxfam bosses who repeatedly apologised to MPs for how the charity handled an internal investigation into the use of prostitutes by staff in Haiti.
Oxfam had been in the country helping it recover from the devastating 2010 earthquake, three years before Mr Goldring was appointed.
Four staff were fired for gross misconduct and three others resigned, including then country director Roland Van Hauwermeiren.
Winnie Byanyima, executive director of Oxfam International, told the committee: "Some hideous men came into our organisation and abused the trust of the British people, the supporters.
"But they were able to get away, to get a recommendation to leave. This was wrong."
Mr Goldring also said that Oxfam had received 26 allegations of misconduct since the scandal was made public two weeks ago, 16 of them overseas and some of them historical.
He said: "We now have to work very hard to earn back the trust of the public. We won't do that by words, but by deeds."
Save The Children chief executive Kevin Watkins was also questioned by MPs and said the organisation had 193 "child safeguarding challenges" in 2016, the latest figures he had.
Stressing that the figures were "tentative", he said that 53 of those were taken to full investigation, 20 of those files were handed to police and 11 people were fired.
"The difficult thing to know in these circumstances is whether you're catching the tip of the iceberg or the iceberg itself," he added.
There were 35 cases of sexual harassment reported at Save The Children International last year and around 19 of those resulted in staff being fired, Mr Watkins said.
Save The Children's director of child safeguarding, Steve Reeves, warned that aid organisations were being targeted by "predatory men" looking for easy access to vulnerable victims.
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Mr Reeves described this as a "very considerable problem", adding: "We know there are large numbers of these people and we know they will seek access to organisations which appear to be weaker and work with children in regions where protections appear to be poorer."
He said that aid organisations "should behave as if that abuse is happening and put measures in place…even if we see no evidence of it".