Kerri Wilkinson, a former tutor in information technology and business studies at the college, has alleged that she was given leaked exam questions and instructed to "focus" students on the answers.
In response to the exam allegations, Alistair Somerville Ford, chief executive of the Institute of Commercial Management (ICM), which set the exams for the Management Information Systems course, said: "The institute's education committee has investigated the allegations of examination irregularities made by the former member of staff at the college and is satisfied that the allegations have substance."
The privately-run college, in the heart of Oxford, takes more than 100 foreign and British students each year for part-time and full-time management, marketing and secretarial courses.
The ICM immediately withdrew the "Approved Centre" status of the private college and decided not to mark students' exam scripts. The ICM candidates will resit the exams free of charge at a different college in Oxford.
In separate allegations made to the GCSE examining body London Edexcel Foundation, Ms Wilkinson, who has since resigned from Oxford Business College, alleged that she had been put under pressure to write one of her student's essays as part of vital coursework. The Spanish student was supposed to attend lessons twice a week with Ms Wilkinson, but invariably failed to attend.
Ms Wilkinson says she refused to write the essays after coming under pressure. She was allegedly told that students had paid a lot of money to attend the college and it was owed to them. The student then sat her final exam on her own in a locked room and was invigilated by a member of staff.
She claims she saw the staff member and student switch seats, giving the impression that until that point, the staff member had been doing the student's exam.
Mike Howlett, Edexcel's head of administration, said: "Edexcel has launched an inquiry into these allegations and until it is complete, it is impossible to comment."
Stanley Hunter, the principal, speaking on behalf of the college, has vigorously denied both sets of allegations. He told The TES: "I refute the allegations that have been made. There is no substance in them. I am not going to say anything more because there is nothing more to say."
ICM has yet to decide where the students will resit their exams.
Oxford Business College will now have to reapply for the "Approved Centre" status.
The college would not reveal the cost of taking the Management Information Systems course.