The university's congregation - which is made up of academics and administrative staff - voted down a call to axe the retirement age.
Paul Ewart, a 69-year-old professor of physics at Oxford, said it was "disappointing... but not the end".
Oxford University said its rule created "career progression" and "inter-generational" fairness.
Prof Ewart has described the rule as "age discrimination" and said it affected many colleagues still teaching at "the peak of their form".
He said he and his colleagues respected the vote but individuals could still take their cases to employment tribunals.
Gill Evans, emeritus professor at Cambridge University, who has been involved in the Oxford campaign, said: "Nobody is surprised, everybody involved sees this as a stage in the process."
The Equality Act prevents employers from forcing workers to retire at 65, although employers can still implement a compulsory retirement age where they can justify it.
A motion to scrap the university's rule was debated by Oxford's congregation on 16 May, but was lost by 143 votes to 64.
Campaigners then triggered the postal vote of all members the congregation - around 5,000 in total - over the future of the EJRA.
The ballot closed on Friday but was defeated by 1,142 votes to 538.
Oxford University said the postal vote was the sixth time in three months that the congregation had considered the "employer-justified retirement age" and that it had supported the policy every time.
"By any standard, the frequency of discussion and voting has been exhaustive and the considerable majority against abolition speaks for itself," it added.
Academics at Oxford University have failed in a new bid to challenge rules forcing them to retire at 67.