In January, there were almost 1,000 reported vacancies in secondary schools, 233 of which were in maths. London accounted for 77 unfilled posts, with a further 30 in Kent and Essex.
The other major shortage subjects were science (156 vacancies), English 129), design and technology (110) and languages (107).
Ms Morris was replying to a question from Plaid Cymru MP Elfin Llwyd. She said that the number of teachers in maintained schools increased by 6,900 between January 1998 and January 2000.
However, a survey by the Department for Education and Employment during the first week of last September showed that there were still around 1,000 vacancies.