A total of 18,422 entries were recorded in 2018.
Despite the drop, the number is still up by 65 per cent on the number of entries in 2003.
Those working within religious education say they're concerned by the declining numbers at a time where community cohesion is needed more than ever.
The decline is being attributed to schools and government not prioritising the subject.
Ben Wood, Chair of the National Association of Teachers of RE (NATRE), said: "It is very disappointing to see that the number of entries has dropped by over 20 per cent.
"This devastating fall has been expected given successive policy decisions that have failed to maintain and support the position of RS as part of a broad and balanced curriculum."
Rudolf Eliott Lockhart, Chief Executive of the Religious Education Council of England and Wales (REC): "At a time when our increasingly diverse society makes high quality religious education more important than ever, it is deeply concerning to see such a dramatic fall in the number of Religious Studies A level entries."
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