About 70 staff and 32 students will be affected by the closure of Redhill College in Surrey, which runs courses for students who are visually impaired or have learning disabilities.
Staff and parents joined members of the University and College Union, the further education trade union that represents tutors at the college, for the protest at the RNIB's London office.
The union said it had "no confidence in RNIB management" and accused the charity of asset-stripping. Management invited the protesters in to hear their views, but said afterwards it would not change its mind.
The decision will bring an end to further education courses at Redhill, such as IT, business administration and employment skills. A community living project will remain at the site.
The RNIB said the decision was made partly because of regional placement policies that restricted the charity to recruiting students locally. This meant it was struggling to get enough students, particularly among the visually impaired population, which accounted for just 25 per cent of pupils at Redhill.
"There aren't enough blind and partially sighted students to justify Redhill," said Eamonn Fetton, group director of direct services at the RNIB.
He added that the education funding body the Learning and Skills Council paid insufficient fees for the students, which meant the charity had to top up their costs.
"We are happy to invest in the development of buildings, but don't feel it would be appropriate for us to subsidise the state," he said.
The charity hopes to sell half of the land at the college's 14-acre green-belt site. But Fetton rejected claims that this was the real reason for closing the college.
He said: "We will dispose of part of the site, but we will be rebuilding on the central part, providing new community houses."
Fetton denied that the RNIB's other further education college in Loughborough was at risk of closing, but admitted it "faced challenges".
Sasha Callaghan, a member of UCU's national executive committee, said: "This is a clear case of asset stripping and an abdication of responsibility by the RNIB board. It is hypocritical when the Government is encouraging welfare to work to take away these students' only route into work."
The union wants the RNIB to review its decision to close Redhill and explore alternative roles for staff employed there.